chapter 1 introduction - university of...
TRANSCRIPT
1
CHAPTER 1
INTRODUCTION
Human interaction with the Earth’s systems has been a very helpful one for ages. Recently,
this interaction has become more intense than ever. This intensified interaction is caused by
the accelerated socio economic development involving population growth (Johari et al.,
2012). Increase in population brought about changes in technology, trade, production and
consumption patterns, and governance among others. As a result, our natural resources such
as minerals and crude oil are being increasingly consumed. Urbanization has also led to
wide-ranging land use practices across the world food security. Desertification, soil erosion
and degradation, looming consumption and exhaustion of our fossil fuel reserves are
contemporary and increasing problems. For example, fossil fuels produce approximately 90
% of the energy we need. Therefore, there is so much dependence on fossil fuel (Johari et
al., 2012). Globally, there are about three major interrelated problems that seriously
threaten our world and civilization; Climate change (due to accumulation of greenhouse
gases in the atmosphere), waste disposal and the need for renewable and environment
friendly sources for energy (IPCC, 2011).
1.1 Climate Change
From observations on global average air and ocean temperatures, widespread melting of
snow and ice and rising of sea levels, it is evident that global warming causes change in
climate. During the last 50 years, the surface temperature of the earth has been on the
increase 0.10 – 0.16 °C per decade. Sea levels have also risen at an average of 1.8 mm.yr-
1(1961- 2003) to 3.1 (1993 – 2003). Arctic sea ice extent has shrunk by 2.7 % per decade
2
with larger decreases in summer of 7.4 % (IPCC, 2007). An increase in the intense tropical
cyclone activity in the North Atlantic since 1970, Pakistan floods (2010), China floods
(2011) can be attributed to the Oceans taking up over 80 % of the heat being added to the
climate system (IPCC, 2011, 2007).
Several studies have been conducted and results have shown that accumulation of
greenhouse gases (GHG) in the atmosphere are likely caused by global warming and
climate change (IPCC, 2011; Stern, 2006). Carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O) and halocarbons (gases containing chlorine, fluorine or bromine) are the main
GHGs (IPCC, 2007). The global atmospheric concentration of these gases have increased
from a preindustrial (1750) values of ~ 280 ppm to 379 ppm, 715 ppb to 1732 ppb and 270
to 319 ppb in 2005 for CO2, CH4and N2O respectively (Stern, 2006; IPCC, 2007).
The main contributor to climate change is CO2. This is because it is the most abundant
anthropogenic GHG in the atmosphere (Stern, 2006; IPCC, 2007). As of June 2011
CO2produced from fossil fuel was 390 ppm at an average increase of 3.3 ppm/yr. CO2
emission has been projected to reach 560 ppm if no action is taken to control it. This could
double the concentration of GHG in the atmosphere by 2035. With a subsequent rise in
temperature that could surpass 5°C which is above the maximum of 2oC preindustrial levels
target. This would mean serious major impacts on physical geography of the earth and on
peoples’ lives (Fig. 1.1). It would also mean that the world’s major coastal cities would be
lost (Stern, 2006). Economically, our current activities will have an effect in the next 40 to
50 years. If transformed into cost, there shall be a high global gross domestic product
(GDP).yr-1 of 5 – 20 % if we fail to act now. Also floods, droughts, storms etc will be
3
affecting the poorest countries and populations. But if we act now, the cost would imply an
estimated 1 % of global GDP/yr and bring stabilization (Stern, 2006). The search for
alternative energy is no more just an attractive option but is inescapable goal of human
civilization.
Figure1.1 GHG emissions by source of CO2eq (IPCC, 2007).
1.2 Waste Disposal
All stages of the materials cycle (extraction, consumption and waste treatment) in urban
and rural areas involves waste generation. The environment is impacted by the way this
waste is managed and the amount of waste generated. For instance, human health is
impacted by the way emissions in the landfills or refineries are managed. Important waste
streams such as municipal solid wastes (MSW) and agricultural wastes have potentially
high environmental impacts. When compared to other waste types, they are rich in organic
biodegradable materials. They can decompose anaerobically or aerobically to generate
methane (CH4), CO2and toxic leachate (Sathaye et al., 2011). The food consumption pattern
25%
14%
8%18%
14%
18%3%
Power
Transport
Buildings
Industries
Agriculture
Landuse
Waste
4
of a city can change with an increase in the income of that city (Troschinetz and Mihelcic,
2009). This increase will cause some changes in waste types and quantities which will pose
a greater challenge for the municipalities to handle. If waste was seen as a resource and
managed rightly, the increase in the volumes of waste would not be a problem. This is
because the more the cities generate waste, the more diversified products they will have.
This increase in produce will mean increase in revenue and a subsequent increase in cost of
living. This could lead to a sustainable development.
According to the Hoornweg and Perinaz, (2012) report sustainable development is one that
meets the needs of the present without compromising the ability of future generations to
meet their own needs (Hoornweg and Perinaz, 2012). According to the report, sustainable
development suggests that meeting the needs of the future depends on how well we balance
today’s decision making as it concerns our social, economic, and environmental needs (Fig
1.2).
Figure 1.2: Objectives of Sustainable development Source: (Hoornweg and Perinaz, 2012)
Services
Household needs
Industrial Growth
Agricultural Growth
Efficient Use of labor
Equity
Participation
Empowerment
Social Mobility
Cultural Preservation
Biodiversity
Natural Resources
Carrying Capacity
Ecosystem Integrity
Clean air and Water
So
cia
l
Economic Environment
5
Sustainable development does not make the world ‘ready’ for the future generations, but it
establishes a basis on which the future world can be built. A sustainable energy system may
be regarded as a cost-efficient, reliable, and environmentally friendly energy system. This
is because it can effectively utilize local resources and networks. It is not ‘slow and inert’
like a conventional energy system, but it is flexible in terms of new techno-economic and
political solutions.
1.3 Renewable Energy (RE)
Globally, it is estimated that RE accounted for 12.9 % of primary energy supply in 2008
(Jagadish et al., 2011). The largest RE contributor was biomass (10.2 %). In as much as the
modern use of biomass is on the increase, roughly 60 % of the biomass fuel are used in
traditional cooking and heating applications in developing countries. In 2009, a rapid
increase was recorded in use of RE despite global financial challenges. This includes;
hydropower (3 %, 31 GW), geothermal power (4 %, 0.4 GW), solar hot water/heating (21
%, 31 GW), wind power (32 %, 38 GW) and grid-connected photo voltaic (53 %, 7.5 GW)
(REN21, 2011). About 2% of global road transport fuel demand was met from Biofuels in
2008 and approximately 3 % in 2009 (Jagadish et al., 2011). From 2008 to 2009, 140 GW
of the approximate 300 GW of new electricity generating capacity added globally came
from RE additions. By the end of 2009 developing countries contributed 53 % of global RE
power (IPCC, 2011). The use of RE (excluding traditional biomass) in meeting rural energy
needs is also increasing, including small hydropower stations, various modern bioenergy
options, and household or village PV, wind or hybrid systems that combine multiple
technologies (REN21, 2011).
6
1.4 Problem Statement
Organic component is about 40% - 60% of the MSW stream of any developing countries.
This translates to about 520 million tonnes of MSW stream out of 1.3 billion generated
globally (Hoornweg and Perinaz, 2012). It is quite obvious that if this can be diverted to
resources then we shall have less waste to handle. There has been several technological
means developed to divert solid waste typically destined for a landfill. They include;
incineration with energy production, composting of organic waste, and material recovery
through recycling. These technologies have the potential to be more sustainable methods to
manage MSW than through landfill.
These technologies so far have the potential to emit CH4 and CO2 gases which are
greenhouse gases. In order to protect our planet and ourselves, action has to be taken to
curb adverse climate change by reducing CO2 and CH4 emission which in turn will reduce
global warming. However, it is also of paramount importance that the problem of waste
management will also be resolved. A solution to this lies in finding a source of biofuel
which is
1. Economically competitive,
2. non-toxic
3. Abundant on earth, and
4. environmentally friendly is needed
Bio-hydrogen seems to fulfill all these requirements, thus this research is based on the
production of bio-hydrogen using food waste through anaerobic fermentation. At
approximately 1ppm by volume H2 is an invisible and a nontoxic light gas that is very rare
in the atmosphere. H2 reacts with other elements quickly because it is very reactive; it does
7
not occur freely in the atmosphere but it is present in water, hydrocarbons, natural and
artificial compounds and in living organisms. H2 has an energy content of 285.9 KJ.mol-1
which is 2.7 times higher than that of gasoline and the combustion of H2 yields heat and
water as by products (Armaroli and Balzani, 2011).
Table 1.1 shows that with the exception of hydrogen, other energy sources have direct
emission of carbon dioxide. It also shows hydrogen to have a higher EE, LHV and higher
fuel to energy conversion. It also shows the high conversion efficiency of hydrogen
technology when compared to that of coal, natural gas, gasoline, diesel and ethanol.
Use of fossil fuels has caused more harm than good to the environment and the world at
large. Their combustion emits greenhouse gases which depletes ozone layer and causes
drastic climate change. The world therefore seeks for an alternative source of fuel which
will be renewable and environmental friendly.
Table1.1 Advantages of hydrogen as a fuel for electricity production over other fuels
Fuel LHV
[MJ/kg
fuel]
Fuel–to-electricity
Conversion
EE
[MJ/kg
fuel]
Direct CO2
emission [kg
C/kg fuel]
Technology Typical
efficiency[%]
Hydrogen 120 FC 65 78 0.00
Coal 15-19 CCPP 58 8-11 0.50
Natural
Gas
33-50 CCPP 58 19-29 0.46
Gasoline 42-45 ICE 33 13-15 0.84
Diesel 43 ICE 33 14 0.90
Ethanol 21 ICE 33 7 0.50
LHV-lower heating value; EE-electrical energy; FC-fuel cell; CCPP-combined cycle power
plant; ICE-internal combustion engine (Marbán and Valdés-Solís, 2007).
8
1.5 Objectives of The Study
1. To enhance food waste degradation through dark fermentation.
2. To ascertain the optimum temperature and pH for bio-hydrogen production
3. To assess the effectiveness of acclimatization in bio-hydrogen production.
4. To determine hydrogen production potential using Gompertz kinetic model.
9
Chapter 2
LITERATURE REVIEW
2.1 Introduction
Most human activities have always generated waste. When human population was
relatively small, this was not a major issue but with urbanization and population increase, it
has become a serious issue. It is estimated that two-thirds of the world’s population will be
living in the cities by 2025 (Mars et al., 2010). This simply means that more resources will
be used up and more waste will be generated. Urban population in developing countries
grows by more than 150,000 people every day (Mars et al., 2010). When this urbanization
is not planned it can be seen on the streets. For example, there will be problem of public
space encroachment, riverbank encroachment, air and water pollution and solid waste
generation (Mars et al., 2010).
2.2 Municipal Solid Waste
Since the formation of non-nomadic societies around 10,000 BC humans have been mass
producing solid waste (Worrell and Vesilind, 2012). Small communities bury their solid
waste just outside their settlements. Some of these communities dispose them into the
nearby water bodies. These practices led to spread of disease and foul odor as population
increased (Seadon, 2006). The accumulation of these waste led to people living in filth in
these growing communities. The ancient city of Mahenjo–Daro in the Indus Valley by 2000
BC, implemented solid waste management processes (Worrell and Vesilind, 2012). Many
other initiatives were implemented in cleaning up the streets. All these were possible when
certain factors like public health and the environment were considered. Other factors
10
include scarcity of resources and the value of waste, public awareness and participation,
and climate change (Worrell and Vesilind, 2012).
2.2.1 MSW in Malaysia
The rate of municipal solid waste (MSW) generation in Malaysia varies from 0.5–0.8 to
1.7 kg/person/day (Manaf et al., 2009). The daily MSW generation has also been on the
increase from 16,200 tonnes (t) in 2001 to 19,100 t in 2005, 17,000 t in 2007 to 30,000 t in
2008, 31,000 t in 2012 and 33,000 in 2013 (Manaf et al., 2009; Omran et al., 2009; Fauziah
and Agamuthu 2008; Agamuthu, 2014; Abdul Rahman, 2013). The acceleration of waste
generation in urban areas such as Kuala Lumpur as shown in Fig 2.1 was due to the
increase in urban population from 6.05 million in 1988 to more than 16.5 million in 2007.
In 2009, it was shown that Selangor and Kuala Lumpur was the highest generator of waste
(Agamuthu, 2009). Kuala Lumpur, the, the capital city of Malaysia, showed increasing
trends of waste generation since 1970. From Fig 2.1, it can also be seen that waste
generation increased by approximately 300 % from 98.9 tonnes/day in 1970 to 311
tonnes/day in 1980 (Agamuthu, 2014). Up till now, the waste generation in Kuala Lumpur
has increased from approximately 590 in 1990s to 3,000 tonnes/day. The total sold waste
generation in Peninsular Malaysia was 5.6 million tonnes or 14,000 tonnes/day and of this
80% was domestic waste while the remaining 20 % was commercial waste (Agamuthu,
2014).
However, it is important to know the composition of waste because the best management
option to adopt will depend on it (Johari et al., 2012). Waste characterization also allows
for the estimate of biodegradable components. It also helps to monitor the effectiveness of
11
programs designed to divert biodegradable and compostable materials from landfills
(Zheng, 2005).
Figure 2.1 Annual Waste Generation in Kuala Lumpur. *- estimated figure
Source: (Agamuthu, 2014)
Table 2.1 shows the changing pattern of waste generation in Malaysia. The percentage of
food waste has been on the increased from 37 % in 2004 to 59 % by 2009 (Noor et al.,
2013), however, the amounts of paper and plastic has shown a substantial decrease. The
large percentage of biodegradable organic matter (food waste and paper) creates a favorable
environment for methane generation as well as hydrogen generation.
0
500
1000
1500
2000
2500
3000
3500
4000
1970 1980 1990 2002 2006* 2009* 2010* 2012*
Soli
d W
ast
e gen
erate
d (
ton
nes
/day)
Year
Annual Waste Generation in Kuala Lumpur
12
Table 2.1 MSW Composition in Malaysia
Source: (Noor et al., 2013). NA Not Available
2.3. Global MSW Generation
Globally, MSW is the most complex solid waste because it is not homogenous as opposed
to industrial and agricultural activities (Noor et al., 2013). Global MSW generation levels
are approximately 1.3 billion tonnes per year which equates to a daily generation rate of 3.6
million tonnes, and are expected to rise by 2025 approximately to 2.2 billion tonnes per
year. This represents a significant increase in per capita waste generation rates, from 1.20 to
1.42 kg per person per day in the next fifteen years. Worldwide, the percentage of urban
residents as a share of the global population is expected to increase to 70 % to 80 % in the
coming decades leading to a growing amount of MSW to be managed (Hoornweg and
Perinaz, 2012).
Material Composition (%)
2004 2005 2006 2007 2008 2009
Food/organic 59.2 36.6 37.43 68.67 57 45
Plastic 12.6 30.7 18.92 11.45 15 24
Paper 8 8.9 16.78 6.43 17 7
Textile 1.4 1 8.48 1.5 1 NA
Wood 2.3 0.3 3.78 0.7 NA NA
Yard waste 7.6 6.7 3.18 NA 5 NA
Rubber 0.7 NA 1.32 NA 1 NA
Glass 1.6 2.8 2.68 1.41 1 3
Organic fines 4 NA 4.37 NA 1 NA
Aluminium/metals 2.4 12.1 3.4 2.71 2 6
Others NA 0.9 7.16 7.13 NA 15
13
From Table 2.2, it is evident that with increase in population, waste generation in all
regions will almost double by 2025. Increase in urbanization is highly correlated with
increase in income level. As disposable incomes and living standards increase, the
consumption of goods and services simultaneously increases, as does the amount of waste
generated (Outlook, 2012; Shekdar, 2009). Globally, MSW costs are expected to increase
from today’s annual $ 205.4 billion to about $ 375.5 billion in 2025 (Hoornweg D. and
Perinaz, 2012).
Table 2.2 Current Urban Waste Generation and Future Projections
Region
Current Available Data Projections for 2025
Total
Urban
Populatio
n
(millions)
Urban Waste
Generation
Projected population Projected Urban
Waste
Per
capital(kg
/capital/d
ay)
Total
(t/day)
Total
Populatio
n(million
s)
Urban
Populatio
n(million
s)
Per
Capita(
kg/capi
tal/day)
Total(t/d
ay)
Africa 260 0.65 169.119 1,152 518 0.85 441,840
EAP 777 0.95 738,958 2,124 1,229 1.5 1,8565,3
79
ECA 227 1.1 254,389 339 239 1.5 354,810
LCA 399 1.1 437,545 681 466 1.6 728,392
MENA 162 1.1 173,545 379 257 1.43 369,320
SAR 426 0.45 1,938 1,938 734 0.77 567,545
EAP – East Asia And Pacific region, ECA – Eastern Central Asia, LCA – Latin American
and the Caribbean, MENA – Middle East and North Africa, SAR – South Asia Region
Source: (Hoornweg and Perinaz 2012)
14
2.4 Global MSW Composition
MSW composition is influenced by the level of available income for goods and services,
local culture, climatic conditions, geographical locations and energy sources (Chinellato et
al., 2013). Geography influences waste composition by determining building materials for
instance wood versus steel, amount of street sweepings and horticultural waste. The extent
of reduction, reuse and recycling (3R's) programs and also the duration of year are also
some factors that can influence MSW composition (Chinellato et al., 2013). MSW
composition influences how often waste is collected and how waste is disposed
(Hoornwegand Perinaz, 2012)
Waste composition in MSW varies widely in different regions and countries. It is evident
from Figure 2.2 that MSW comprises mainly of organic waste, followed by paper, metal,
other wastes, plastic, and glass. Generally the biodegradable portion is mainly due to food
and yard waste, typical of the developing countries. The high paper and plastic content is
typical of developed countries which could be as a result of purchasing prepared food, lots
of office work and high recycling rate (Karak et al., 2012). When disposed in a landfill, it
generates leachate which might seep into aquatic water bodies causing water pollution or
into land causing land pollution. Furthermore, in benthic environment, leachate constituents
can accumulate in poorly ventilated hypoxic and anoxic interstitial waters. Here,
leachatemay be directly assimilated by benthic organisms; it could lead to death of the
organisms. It could be said to cause nuisance to the society (Tomczak-Wandzel, 2013).
Although MSW composition is generally provided by weight, as a country increase in
affluence, she tend to pay more attention toher waste volumes, particularly with regard to
15
collection: organics and inerts generally decrease in comparative terms, while increasing
paper and plastic increases overall waste volumes (Hoornwegand Perinaz, 2012)
Figure 2.2 Global Solid Waste Composition(Hoornweg and Perinaz, 2012)
Source: eawag: Swiss Federal Institute of Aquatic Science and Technology
2.5 Solid Waste Management Practices
Increased generation and complexity of MSW has led to the development of many methods
to help in its management. They are;
i) open dumping and landfilling,
ii) Biological treatment (composting and anaerobic digestion (AD) )
iii) 3 R (Reduce, Reuse and Recycle)
iv) Thermal treatment (Incineration and Pyrolysis)
Organics, 46%
Paper, 17%
metal, 4%
Glass, 5%
Plastic, 10%
Other, 18%
Global Solid waste Composition
16
i) Open Dumping and Landfilling
This is a primitive type of waste disposal. It is the most cost effective method in many
developing countries. Open dumping is basically, a situation where waste is dumped in a
place and not covered with soil or other materials. This attracts flies and scavenging
animals, thus, it is does not have aesthetic value. This method is commonly seen in
developing countries such as India, Bangladesh, Most African countries and South East
Asian countries (Agamuthu, 2001; Parrot et al., 2009).
A landfill is a carefully engineered depression in the ground (or built on top of the ground,
having the resemblance of a football stadium) into which wastes are put by burial.
Fundamentally, a landfill is a bathtub in the ground and a double-lined landfill is one
bathtub inside another. Out the bottom is the leaking of leachate produced as a result of the
decomposition of the organic matter. Leakage at the top is the release of gases such as CH4,
also produced due to the decomposition as well (Hoornweg and Perinaz, 2012).
ii) Composting and Bio-gasification
Composting is a process that involves the biological decomposition of organic matter,
under controlled operation to produce a humus-like stable product (Worrell andVesilind
2012). The basic composting process is given in the following equation:
[Organic complex materials] + O2 -------------> CO2, NO2, NO3 (1)
The aerobic microorganisms’ extract energy from the organic matters through a series of
exothermic reactions that break the material down to simpler materials as shown in the
Aerobic
(Oxidation)
17
equation above. For a proper function of a composting operation, non-compostibles such as
metals, glassware and ceramic items must be removed(Worrell and Vesilind 2012).
Bio-gasification, on the other hand, is anaerobic and the breakdown process is reduction.
The products are mainly CH4 and CO2 as shown below
Organic compounds -------------> CH4, CO2------------------------ (2)
According to Agamuthu (2001), composting has four main objectives, which are; volume
reduction, stabilization, sanitization and valorisation (includes compost and biogas). On dry
weight basis, up to 75 % of the oraganic material could be decomposed while the weight
loss of wet agrowaste is around 50 % (Agamuthu, 2001).
iii.) 3R (Recovery, Reuse and Recycling)
Reuse/Recycling refers to the collection and separation of waste and their subsequent
transformation into usable or marketable materials (Nakahashi, 2008). For instance, plastic
wastes can be used as feedstock in coke ovens or blast furnaces in iron and steel
production. Plastic waste or a mixture of waste plastics and paper can substitute coal in
boilers or kilns. Steel, cement and paper industries which are energy intensive industries are
more effective in using recyclable wastes as feedstock or fuel in their production
(Nakahashi, 2008). Recycling has major advantage of reducing the quantities of disposed
waste and also returns materials to the economy (Daniel and Natalie, 2005). The use of
recycled materials in inductries reduces energy use and emissions; lessens impacts when
raw material is extracted and conserves raw materials (Agamuthu, 2001).
Anaerobic
(Reduction)
18
2.6 Thermal Treatment
As the name implies, it involves the use of heat in combusting waste. It could be solid,
liquid or gaseous. There are two major processes here, which are incineration and pyrolysis
(Agamuthu, 2009). In a broader sense, waste materials are treated at incinerator plants
through the controlled application of heat that converts waste feed by high temperature
oxidation to gaseous materials emitted as flue gas, viscous waste (slag) and solid residue
(ash). During combustion, the moisture is vaporized while the combustible waste is also
vaporized and oxidized resulting in the final products CO2, water vapor, ash and non-
combustibles or residue (Agamuthu, 2009).
2.7. Waste to Energy
While waste is generally perceived as a nuisance, it has hidden value as an energy fuel. One
tonne of MSW can produce 535 kWh of electricity through incineration (Percy et al.,
2012). This implies that, waste can become a resource. On the other hand, CH4 gas is
generated when organic waste dumped in the landfill decomposes. This CH4 gas can be
trapped and used to produce energy. CH4 gas is also produced during the decomposition of
livestock and human waste and can be trapped from these sources. Landfill gas collection
systems can be installed at landfills to capture the CH4 produced by trash as it decomposes
(Dann et al., 2012).
2.7.1 Why Convert Waste to Energy?
Energy is the driving force that sustains our lifestyle. All our activities such as economic,
physical and social welfare depends on it. The continuous supply of energy with an
increasing worldwide demand institutes a significant challenge for our society. About 78%
- 87 % of this energy demand has been met mainly through the exploitation of our natural
19
reserves of fossil fuels (oil, coal, gas). As reported in 2012, global energy consumption
was predicted to increase from 534 quadrillion joules in 2010 to 819.7 quadrillion joules in
2040 (Outlook, 2012) as shown in Fig 2.3. As of January 2006, it was reported that the total
global natural gas reserves was 6112 trillion m3, while 95 trillion m3 has been consumed as
of 2003 (EIA, 2011). Without considering the increase in demand, this would suggest that
in approximately 60 years, natural gas will run out. Natural gas remains an important fuel
for electricity production. This is because it is less capital intensive than those using coal,
nuclear or most renewable energy sources. Global consumption of natural gas is projected
to increase by 1.3 % per year from 108 trillion m3 in 2007 to 156 trillion m3 in 2035 (EIA,
2011).
Cars that run on petrol can be easily converted to run on natural gas. Natural gas and coal
are used as raw materials to produce heat and electricity whereas oil serves dual purposes.
The non-OECD countries are the highest energy consumers (Fig 2.3). This could be
because most of these countries are developing and under-developed nations who do not
have sufficient funds to use the recent energy reduction technologies (Outlook, 2012).
In the petroleum sector, the global demand for oil is on the increase, the petroleum industry
has experienced about 30 % spike in oil use. Thus, on daily basis, it is becoming clearer
that sustainability cannot be achieved by the current energy resources (Baxter, 2005).
20
Figure 2.3 World energy consumption by OECD and non-OECD countries
Source (EIA, 2011) * - Prediction, OECD – Organization for Economic Cooperation and
Development countries.
Coal contributes more than one-fourth of the world's total primary energy supply and more
than one-third of the fuel used for electricity generation. Coal provides the largest share of
world electricity generation which was 42 % in 2007 and remains unchanged through 2035
(EIA, 2011). The general fuel consumption is on the increase (Outlook, 2012).
Incomplete combustion processes, which result from the burning of fossil fuels produced a
great amount of gases as carbon dioxide (CO2) and nitrogen oxides (NOx). CO2 emissions
are of particular concern, since CO2 has been identified as a GHG. The atmospheric
concentration of GHGs has been steadily rising. In 2005, the concentration of CO2 rose to
378.9 ppm (Hou et al.,2013). This increase has been directly linked to human activity such
as bush burning, transportation etc.
0.0
100.0
200.0
300.0
400.0
500.0
600.0
1990 2000 2010 2020* 2030* 2040*
Qu
adri
llio
n J
ou
les
Year
World energy consumption(quadrillion Btu) Non-OECD
World energy consumption(quadrillion Btu) OECD
21
World nuclear power is expected to increase from 2.6 Trillion Kw/h in 2007 to an estimated
4.5 Trillion Kw/h in 2035 (Arvizu et al., 2011). Despite this fact, countries such as China,
India and Russia accounts for the largest increase in world installed nuclear power with 114
Gigawatts of nuclear capacity of which 60 % belongs to China alone (Outlook, 2012).
From the Table 2.3, it is evident that the natural reserve will decrease with increasing
consumption. In order to meet the demand of the increasing population, more of the natural
will be used up and we shall face scarcity in the mere future. Therefore, there is the need to
transform our current fossil fuel dependent energy systems to new clean renewable energy
sources. These renewable energy sources include: Bioenergy, direct solar, geothermal,
hydropower, wave and wind energy (IPCC, 2011).
Table 2.3. World fossil fuel reserve and consumption in 2009
Oil Natural Gas Coal
World Reserves (M barrels)
1.333 x 1012
(T M3)
187.5
(M tonnes)
826001
Consumption (M barrels/day)
84.1
(B M3/year)
2940.4
(M tonnes/year)
3278.3
R/P Years
45.7 62.8 240
Source (BP 2010). R/PProduction Ratio
2.8 Technologies for Sustainable Energy Production
Hydropower is a renewable resource from the global water cycle, driven by the sun. It is
basically the conversion of water's potential (or kinetic) energy into electricity using water
turbines and electric generators. Globally, between 40,000 and 50,000 large dams have
22
been built for different purposes such as irrigation, domestic water use, flood control, and
power generation (Balmer and Spreng, 2008). Hydroelectric power is a major source of
renewable energy growth in developing countries. For example, China, India and Brazil
collectively accounts for 83 % of the total increase in hydroelectric production (Kumar and
Schei, 2011).
On one hand, photovoltaic, wind and biomass, among others stand out in their
technological innovation and prospects for future economic development. Alternatively,
today in many parts of the world, civil nuclear power receives support from policy makers
who are willing to expand its use (Cicia et al., 2012). The use of solar energy has rapidly
increased in the past few years (30 – 40 % a year), yet, the current global nature of solar
power output is equivalent to less than 1% of global demand for electricity (Arvizu et al.,
2011). This suggests that the use of solar energy technology faces a big challenge globally.
This is especially in developing and new industrialized countries, which are more oriented
to rapid economic growth and tend to be less sensitive to environmental concerns (Dorian
et al., 2006).
One of the first renewable technologies to be adopted on a large scale is wind energy. As of
the end of 2006, the installed global capacity of wind energy technology was greater than
74,000 MW (Staudt, 2008). The economics of wind energy can be compared with fossil-
fuel technology in the windier parts of the world. A significant percentage of the world's
electricity can be supplied by the vast supply of wind energy resource. The differential
heating of the earth's surface by the sun which causes wind results in low and high pressure
systems as heated air rises and then falls (Staudt, 2008). Around the globe, wind turbines
23
are already providing substantial amounts of sustainable, pollution-free electricity. There is
also a high growth rates for wind powered electricity production in developing nations. For
example, the total generation from wind power plants in China is projected to increase from
6 b KW/h in 2007 to 374 b KW/h in 2035 (Hoornweg and Perinaz, 2012).
2.8.1 Incineration
Waste incineration could be defined as controlled burning of solid, liquid or gaseous waste.
Waste Incineration reduces the volume of waste by about 90% and the remaining ash goes
to landfill (Masirin et al., 2008). These high volume reductions are only seen in waste
streams with very high amounts of horticultural waste, packaging materials, plastics, paper
and cardboards. It offers the solution of waste disposal to countries where land is scarce. It
is also one way to prevent CH4 release from landfills. For each tonne of MSW processed in
a waste incineration plant, 1 tonne of CO2eq is avoided (Dann et al., 2012). US
Environmental Protection Agency has stated that waste incineration plants produce
electricity with less environmental impact than almost any other source of electricity (Dann
et al., 2012). With increasing regulatory focus on GHG emissions, waste incineration turns
from an environmental problem to an environmental solution.
2.8.2 Pyrolysis
Pyrolysis is a thermochemical decomposition of organic materials at elevated temperatures
in the absence of oxygen. It is also an irreversible process. The key products of biomass
pyrolysis are water, permanent gases such as (H2, CO, CO2, and CH4), C2–C3 hydrocarbon
gases, tar and char (Consonni and Viganò, 2012). The formation of tar is the main issue in
biomass pyrolysis. It causes blockage of equipment and fouling of down-stream application
24
process which reduces the thermal efficiency. It is therefore necessary that tar is
decomposed into gas products (H2 and CO) during the pyrolysis of biomass. Generally, the
main method for removing tar is by in situ tar cracking. Operating factors such as catalyst,
reactor structure, heating rate, and temperature and residence time can be enhanced to
maximize the effectiveness of pyrolysis and reduce tar formation (Qinglan et al., 2010).
Air, steam or oxygen can be used as a gasification agent to increase energy value in the
conventional gasification which is an old technology, in which biomass is heated at high
temperatures and separated to combustible gas (Kalinci et al., 2009).
Gasification is simply the process that converts a solid or liquid combustible feedstock into
an incompletely oxidized gas called “syngas” (mostly a mixture of CO, H2, CO2 and H2O).
The term “gasification plant” is commonly used to designate the entire system that converts
the primary feedstock into useful energy carriers. In order to meet the requirements of high-
efficiency, internally-fired cycles (gas turbines, internal combustion engines), proper
syngas treatment is needed (Consonni and Viganò, 2012).
2.8.3 Landfill
A common final disposal site for waste is landfills and should be planned and operated to
protect the health of the public and the environment. The CH4 produced from the anaerobic
decomposition of organic matter can be recovered and burned with or without energy
recovery to reduce GHG emissions. Landfill CH4 represents 12 % of total global CH4
emissions (EPA, 2006). Furthermore, almost half of the CH4 emission attributed to the
municipal waste sector in 2012 comes from Landfill CH4 emission (Johari et al., 2012).
Different countries have different levels of CH4 from landfills depending on waste
compositions and waste disposal practices as shown in Table 2.4. Landfill gas, a by-product
25
of anaerobic decomposition is composed of CH4 (50%), CO2 and other gases. In
comparison with carbon dioxide, CH4 has a global warming potential 21 times greater than
carbon dioxide, and it is the second most common GHG than CO2(Saeed et al., 2013).
Table 2.4 Landfill CH4 Emissions and Total GHG emissions for selected Countries
Country CH4 emissions from
post-comsumer
Municipal Waste
Disposal (MtCO2e)
GHG emissions
(CO2, CH4, N2O)
(MtCO2eq)
% CH4 from
disposal Sites
Relative to Total
GHG Emissions
South Africa 16 380 4.3
Mexico 31 383 8.1
Brazil 16 659 2.4
India 14 1210 1.1
China 45 3650 1.2
According to the ministry of Housing and Local government website, there are generally
296 landfills/dumpsites in Malaysia out of which 165 are still in operation. This includes
eight sanitary landfills (Manafet al., 2009). More sanitary landfills are been planned in the
future either to replace or to upgrade the current dumpsites.
2.8.4 Hydrogen Production
The world has recognized hydrogen as an energy carrier that complies with all the
environmental quality, energy security and economic competitiveness demands. Roadmaps
such as “Hyways Roadmap Europe” by European Commission (EC), “the National
Source (EPA, 2012)
26
Hydrogen Energy Roadmap and the Hydrogen Posture Plan” by the US Department of
Energy (DOE), “The Hydrogen Technology Roadmap” by the Australian Government
Department of Resources, Energy and Tourism and the Future Fuels for the Asia Pacific
Economic Cooperation (APEC), have already been developed as roadmaps to the transition
to “Hydrogen economy (Hyways, 2007; Hurley, 2009; Armaroli, 2011). Hydrogen (H2) is
the third most abundant element on Earth and the most abundant element in the universe
(Armaroli, 2011).
Many technologies have emerged in response to the environmental, economic security and
energy needs. These include;
Hydrogen from Biomass, (Kalinci et al., 2009)
Hydrogen from steam reforming of fossil fuel, (Jean, 2010)
Water Electrolysis, ( thermochemical) (Richard, 2008)
Biological methods (Nathao et al., 2013)
Hydrogen Production from photosynthesis (Allakhverdiev, 2012)
2.8.4.1 Hydrogen from Biomass
Agricultural residues, forest resources, perennial grasses, energy crops, wastes (MSW,
urban wood waste, and food waste), and algae are all biomass. Thus, biomass is an
abundant renewable resource and it is said to be capable of supporting the future H2
economy (EERE, 2011). For example, US department of energy reported that the total
annual biomass consumption for both bioenergy and bio-products is about 190 million dry
tonnes. This provides over 3 % of the total energy consumption in the United States
(EERE, 2011). Among renewable energy resources, biomass has distinctive characteristics
27
which is that in addition to power, it can be converted to carbon based fuels and chemicals
(Kalinci et al., 2009). Thus, biomass stands as the only renewable resource with the
potential to replace fossil based fuels. It is estimated that over a billion tonnes of sustainable
biomass resources are produced in the United States (EERE, 2011). This can provide fuel for
cars, trucks, and jets; make chemicals; and produce power to supply the grid. It also creates
new opportunities and jobs throughout the country in agriculture, manufacturing, and service
sectors.
The composition of biomass varies depending on its nature as shown in Fig 2.4. The most
important components of biomass are starch, cellulose, hemicelluloses and lignin. These are
also among the most abundant renewable resources on earth. Starch, cellulose and
hemicelluloses are potential sources of fermentable hydrolysates into H2, ethanol, butanol
among others. Biomass such as agricultural food and food waste biomass is usually rich in
starch (Sun and Cheng, 2002).
Starch, a main constituent of biomass, is present in many agricultural and staple food
wastes such as potatoes, corn, rice, wheat, pasta and wastes from textile industries (Güllü
and Demirbaş, 2001; Hanaoka et al., 2004). Starch molecules are more susceptible to
enzyme and other hydrolysis systems, thus are easily broken down into glucose (Mars et
al., 2010; Rosendahl et al., 2008). Cellulose, a major component of agro-food wastes is also
one of the most abundant renewable organic compound on earth. Cellulose molecules under
normal conditions are insoluble in water and are strongly resistant to enzymatic attack and
chemicals such as acid compounds. Therefore, cellulose is more difficult to hydrolyze into
glucose units than starch (Vijayaraghavanand Yun, 2008).
28
Figure 2.4:Components of Biomass.Source (Heidrich and Witkowski, 2010).
Waste such as agricultural and agro-industrial wastes not only provides an economical
source of energy but also an effective low sulphur fuel (Capareda, 2011). In order to reduce
environmental hazards, biomass could further be processed into other fuels e.g. biomass
from sewage. Nevertheless, the conversion of light energy into biomass by plants is
relatively of small percentage and there is somewhat low concentration of biomass per unit
area of land and water (Capareda, 2011). Thus, the conversion methods into fuels are
important.
There are different methods for converting biomass into fuel (Fig 2.5). The most efficient
process of these is the conversion into heat energy process (Heidrich and Witkowski, 2010). In
order to have diverse use of biomass resources, they need to be converted into chemical,
electrical or mechanical energy. These take the form of solid fuel (charcoal), liquid fuel
(ethanol) or gaseous fuel (methane). These fuels can be used in a wide range of energy
conversion devices to satisfy the diverse energy needs.
29
2.8.4.2 Hydrogen from Steam Reforming of Fossil Fuels
Steam reforming is a process to reform hydrocarbons in the presence of H20 to produce
syngas using catalyst (supported Ni-based) at a prescribed reaction conditions. As shown in
Fig 2.6, syngas is a mixture of H2, CO and CO2 in various proportions (Jean, 2010). Steam
reformation of fossil fuel accounts for about 96 % of global H2production, of which 49 % is
natural gas, 29% is liquid hydrocarbon and 18% is coal (Matthew, 2009). Steam CH4
reforming (SMR) is highly efficient having about (65 - 75 %) conversion of natural gas into
H2and syngas production (Matthew, 2009).
The integration of separation membranes to the SMR process help to overcome
thermodynamic limitations. It also helps to achieve almost 100 % CH4conversion to H2 at
lower temperatures. Carbon capture and storage (CCS) is seen as a way to reduce CO2
Figure 2.5 Methods of Using Biomass for Energy Source: (Heidrich andWitkowski, 2010)
Biomass Resources
Con
versi
on
Proc
ess
Direct Combustion Heat
Intermediate Fuels (biodiesel, ethanol, gasoline,
etc.)
Heat
Engines Generators Electricity
Mechanical
Power
30
emissions into the atmosphere, thus decreasing the threat of global warming. It involves the
capture and transportation of CO2 to a store location (Basu et al., 2010). Storing and
maintaining the CO2in CCS is currently limited and more research and demonstration
projects to develop efficient and economic methods for carbon capture, transport and
storage needs to be done. With ultimate CCS, SMR is projected to be the main source of H2
to meet up with increasing demand. The problem with this approach is that fossil fuel
power will still emit CO2 through residual emissions from power plants due to limited
capture efficiency.
Figure 2.6 Steam reformation of fossil fuel (Jean, 2010)
2.8.4.3 Steam Reformation of Glycerol
This reforming process is the splitting of hydrocarbons in the presence of water and water–
gas shift reaction as given below (Equation 1)
CnH2n+2 + nH2O→ nCO + (2n+1) H2…………………………………. (1)
31
Stochiometrically, the moles of hydrogen obtained by steam reforming of natural gas is
four, while that obtained from steam reforming of glycerol is seven as equation (2).
Therefore, using stoichiometric study, glycerol will be preferred to fossil fuels because it
provides a higher number of moles of hydrogen.
C3H8O3 (g) + 3H2O (g) ↔7H2 (g) + 3CO2 (g) ΔH = 128 kJ/mol ……………….(2)
However, this process also has some limitations such as control of high temperatures, the
unavoidable CH4 formation, and the formation of coke. The coke formed acts as a poison
and clogs the pores of the catalyst, thus affecting the process, as well as, the yield and
purity of hydrogen (Avasthi et al., 2013).
2.8.4.4 Electrolysis of water
Electrolysis of water is the splitting of water into oxygen and hydrogen gas by passing an
electric current through it. This process requires large amounts of energy thus it is the most
costly method of H2 production (Matthew, 2009; Richard, 2008). The current breaks the
chemical bond between the H2 and O2 thus, splitting them into atomic components.
At the cathode, water combines with electrons from the external circuit to form H2+ and O2
-.
The oxygen ions however, reacts at the anode to form oxygen gas and give up the electrons
to the external circuit (Fig 2.7). The overall environmental friendliness depends on the fuel
source. However, due to the high energy requirement involved in this process, people do
not like to get involved in it(Millet and Grigoriev, 2013).
32
Figure 2.7 Schematic Diagram of Industrial water electrolysis to produce hydrogen. Source:
(Richard, 2008).
2.8.4.5 Bio-catalyzed Electrolysis
This is a process whereby organic matter is converted into hydrogen by the use of
electrochemically active enzymes inside an electrochemical cell via coupled anode-cathode
reactions (Rozendal et al., 2008). This technology is mainly used to generate hydrogen
from wastewater with high organic content.
At the anode, electrochemically active microorganisms oxidize the organic material from
the wastewater. Consequently, the electrons resulting from this oxidation reaction are
transferred by microorganisms to the anode by means of extracellular electron transfer
(EET). The electrons are transported to the cathode, where they are consumed for oxygen
reduction (in the case of MFCs) or product formation (in the case of MECs) via an
electrical circuit. Electro neutrality is maintained in the system by the transport of ions in
33
between the electrodes (optionally through a membrane). In an MFC, electrical energy can
be extracted from the electrical circuit. In an MEC, however, electrical energy needs to be
supplied to the electrical circuit by means of a power supply (Rozendal et al., 2008). See
Figure 2.8
However, MFCs and bio-catalyzed electrolysis systems operate at low current densities (∼1
to 10 A/m2) and as a result, MFCs and bio-catalyzed electrolysis systems produce too little
electricity or hydrogen per amount of platinum. Moreover, the platinum electrode is such
an expensive material as the cathode catalyst. This has encouraged researchers to look for
alternative hydrogen energy source (Renea et al., 2007).
Figure 2.8 Schematic diagram of Bio-catalyzed electrolysis. Source (Rozendal et al., 2008).
Wastewater
Effluent
CO2
An
ode
Cathode
A-
C+
A- C+ e-
H2
CO2
H2 e- e-
Power Supply Organic
matter
e-
34
2.8.4.6 Bio-photolysis-Green Algae/Cyanobacteria
Biological hydrogen can be generated from plants by bio-photolysis of water using
microalgae (green algae and Cyanobacteria). Bio-photolysis is the decomposition of water
by algae or cyanobacteria to hydrogen and oxygen with the aid of sunlight. Photosynthetic
production of hydrogen from water is a biological process that can convert sunlight into
useful, stored chemical energy as shown in equation 3.
2H2O 2H2 + O2…………………………. (3)
This process is attractive because it uses solar energy to convert a readily available
substrate (water), to oxygen and hydrogen. Water splitting involves one enzyme
(hydrogenase) in the case of unicellular algae to catalyze hydrogen generation, while two
enzymes are involved in the case of Cyanobacteria; hydrogenase and nitrogenase to do the
same work of catalyzing the hydrogen generation process. However, this process is not
economically viable because it requires large bioreactor surface area, solar conversion
efficiency of about 10 % and a large reactor foot-print (Matthew, 2009). Moreover, the
oxygen which is generated during the process inhibits the algal hydrogenase(Renea et al.,
2007).
2.8.4.7 Photosynthetic Hydrogen Production
Hydrogen is mainly generated here through the action of nitrogenase enzyme via
photosynthetic bacteria such as Rhodabactersphaeroides. Nevertheless, the presence of
oxygen and excess amounts of ammonia inhibits this activity (Harun, 2003). High nitrogen
concentration has been linked to high biomass concentration instead of hydrogen
35
production. The higher the biomass concentration, the less light that can diffuse into the
bioreactor (Harun, 2003).
2.9 Dark Fermentation
In biological hydrogen production, organic materials are metabolized by bacteria or
microalgae actions to produce hydrogen. Biological hydrogen production generates less
GHG. Furthermore, it reduced the negative environmental impact of biomass residue,
domestic and food industrial waste waters (Hallenbeck, 2009). Dark fermentation is a
biological process performed in anaerobic conditions. The bacteria are grown in the
absence of light sources under appropriate conditions to produce H2 from carbohydrate rich
substrates. Dark fermentation simply put is the fermentative conversion of organic substrate
to bio-hydrogen (Equation 4). The anaerobic degradation of carbohydrates by heterotrophic
microorganisms has several important advantages. The advantages include high rates of H2
production and constant H2 production (during day and night). Fermentative bacteria have a
good growth rate to supply the H2 into the system. The utilization of agricultural and food
industry wastes as resources provides a valuable way to divert these wastes from landfill
(Johari et al., 2012).
C6H12O6 + 4H2O 2 CH3COO- + 2 HCO3- + 4 H+ + 4 H2 ---------------Equation (4)
As shown in Fig 2.9, anaerobic breakdown of organic matter are in four stages; hydrolysis,
fermentation (or acidogenesis), acetogenesis and eventual methanogenesis(Gerardi, 2003).
Hydrolysis involves the conversion of complex molecules and compounds such as
carbohydrates, Proteins and lipids – found in organic matter into simple sugars, amino acids
and long chain fatty acids, respectively (Kalinci et al., 2009). Hydrolysis is a relatively slow
36
process and generally it limits the rate of the overall anaerobic digestion process. The
second step of the anaerobic digestion process is acidogenesis or acidification, this process
results in the conversion of the hydrolyzed products into simple molecules like volatile
fatty acids (e.g. acetic-, propionic- and butyric acid) with a low molecular weight, alcohols,
aldehydes and gases like CO2, H2 and NH3. The acidogenic bacteria are able to metabolize
organic material down to a very low pH of 4 (Valdezand Poggi, 2009).
The third step is acetogenesis. Here, acetogenic bacteria convert the products of the
acidification into acetic acids, hydrogen, and carbon dioxide. This process is affected by
diverse group of bacteria, majority of which are strictly anaerobes. Luckily for these strict
anaerobes, there are always bacteria present that will use oxygen whenever it is available.
The presence of these bacteria is important to remove all oxygen that might be introduced
into the system, for instance together with the excess sludge.
These three stages are called acid fermentation. It is important to note that in the acid
fermentation, no organic material is removed from the liquid phase.
The final step of anaerobic digestion process is methanogenesis. The products of the acid
fermentation (mainly acetic acid) are converted into CO2 and CH4. After this conversion,
the organic material will be removed, as the produced CH4 gas will largely dissolve from
the liquid phase. Methanogens have the ability to produce CH4 by using the carbon dioxide
and hydrogen gas or the acetic acid produced from both the acetogenic or acidogenic
phases. Dark Fermentation is meant to either inhibit or slows down this methanogens and
harvest the hydrogen gas.
37
Figure 2.9 Diagram of anaerobic digestion and dark fermentation.
Source: (Basu et al., 2010)
Anaerobic or dark fermentation is one of the most widely studied techniques of producing
bio-hydrogen. Anaerobic fermentation is known for its rapid hydrogen evolution rate and
does not require large surface area or any external energy. Dark fermentation also yields
other metabolites such as H2 and electricity production, which can be further processed
through microbial fuel cells (Logan and Regan 2006).
38
There are many factors that affect hydrogen production such as microbes, temperature, pH,
type of substrate, reactor type among others.
2.9.1 Microbes
Inoculum sources for fermentative hydrogen production can be classified into two groups:
mixed bacteria cultures from natural sources and pure cultures from bacterial culture
collections. In the natural environment such as soil, wastewater sludge, compost among
others, hydrogen producing bacteria widely exist (Kalogo and Bagley, 2008). Nevertheless,
Clostridium and Enterobacter are most widely used as inoculum for fermentative hydrogen
production. Bacteria of the genus Clostridium form endospores and are gram-positive, rod-
shaped and strict anaerobes, while those of the Enterobacter species are gram-negative,
rod-shaped, and facultative anaerobes (Kalogo and Bagley, 2008; Kraemer et al., 2007).
Some other natural sources that has been used to provide inocula for H2 production by
mixed micro flora, includes; biosolid and biosolid pellets (Fang et al., 2006; Kalogo and
Bagley, 2008; Keigo and Shigeharu, 2006). In order to eliminate methanogens and select
spore formers, inocula are commonly pretreated. There are various pretreatment methods
such as heat treatment, acid and alkali pretreatment (Jayalakshmi, 2007; Kimet al., 2013;
Kraemer et al., 2007).
Heat treatment selects endospore forming bacteria, such as Clostridium, Bacillus and
Thermo-anaerobacterium. However, it inactivates H2-consuming methanogens and prevent
consumption of the produced H2. Nevertheless, a low pH of 5.5 has been reported to control
methanogens (Fang et al., 2006; Kraemer et al., 2007; Mizuno et al., 2000).
39
Alkali-treated sewage sludge (SS) was used as a microbial source for H2 fermentation of
food waste leachate (FWL) and the highest H2 yield of 2.1 mol H2/mol hexose was
achieved at pretreatment pH 10 and a mixing ratio of FWL to SS = 3:5 (Kim et al., 2013). It
was also found that pretreatment pH 9 was not strong enough to suppress the activity of
lactic acid bacteria (LAB) which are the non-H2-producers in SS. Moreover, microbial
analysis showed that LAB such as Lactobacillus sp. and Enterococcus sp. was the
dominant species at pretreatment pH 9 while Clostridium sp., the main anaerobic H2-
producers, were dominant at pretreatment of pH 10 (Kim et al., 2013).
Aged refuse (AR) excavated from a typical refuse landfill with over 10 years of placement
was also used for the augmentation of bio-hydrogen production from food wastes. It was
found that below 0.4% of hydrogen concentration could be detected in the biogas produced
due to its severe acidification properties. However, the hydrogen concentration in the
biogas increased to over 26.6% with pH ascending from 4.36 to 5.81 when AR (50% in
weight) was added. Meanwhile, it was also found that sterilizing the AR by heating at
160 °C for 2 h before being used as additive for bio-hydrogen production from food wastes
decreased the hydrogen content in the biogas drastically to 3.3%. This signifies that the AR
may chiefly function as a microbial inoculum (Li et al., 2008).
Food and microbe (F/M) ratios were analyzed in a two stage process and it was found to
influence biogas yield, production rate, and potential. The highest H2 and CH4 yields of 55
and 94 mL g−1 VS in two stage process and the highest CH4 yield of 82 mL g−1 VS in one
stage process was observed at F/M of 7.5 (Nathao et al., 2013).
40
2.9.2 Temperature
Temperature is one of the most important factors that influenced the activities of hydrogen-
producing bacteria and the fermentative hydrogen production. Akutsu et al, (2009) has
shown that different organisms require different temperature range. Some organisms are
better at very cold environment, while others are better at very hot environment and the rest
are better in between, popularly called moderate organisms (Akutsuet al., 2009). Organisms
can be classified as psychrophilic, mesophilic or thermophilic depending on the
environment they can survive in. It is also important to note that these organisms have some
adaptive features which they possess that make it possible for them to survive in any of
these temperatures. Therefore, if they are removed from their original environment to
another, they may die.
It has been validated that in an appropriate range, the ability of hydrogen-producing
bacteria to produce hydrogen could increase with increase in temperature. Nonetheless,
temperature at much higher levels could decrease hydrogen production with increasing
levels of temperature (Linet al., 2008). However, the optimal temperature reported for
fermentative hydrogen production has not always been the same, but it fell into the
mesophilic range (around 370C) and thermophilic range (around 550C), respectively
(Akutsu et al., 2009; Harun, 2003; Jingwei, 2008; Kim et al., 2013; Lin et al., 2008).
In studying the hydrogen production from food waste by the mesophilic and
thermophilicacidogenic culture acclimated with sewage at 5 days HRT, it was shown that
the biogas produced from the thermophilicacidogenic culture was free of CH4 at all tested
pH and VS concentrations (Shin et al., 2004). It was also shown that from the
41
mesophilicacidogenicculture, CH4 was detected at all tested pH. However, the amount of
hydrogen produced from the thermophilicacidogenic culture was found to be much higher
than that from the mesophilic culture at all tested pH. This could be due to CH4 free
condition and negligible propionate production. Increase of VS concentrations from 3 to 10
g VS−1 caused an increase in quantity and quality of hydrogen produced. The maximum
hydrogen content was 69% (v/v) at 10 g VS−1. The hydrogen yield was in the range of 0.9–
1:8 mol-H2 mol-hexose with the peak at 6 g VS−1 (Shin et al., 2004).
2.9.3 pH
Another important factor that influenced bio-hydrogen production is the pH because it
affects both the metabolic pathway and also the activities of the hydrogenase. Most studies
done on this were done using a batch reactor therefore only the initial pH were of major
concern. It has been shown that in an appropriate range, the ability of hydrogen-producing
bacteria to produce hydrogen during fermentative hydrogen production increased with
increase in pH, nevertheless at much higher levels of pH, the hydrogen producing ability of
the bacteria decreased (Fang et al., 2006; Herbert, 2002; Kim et al., 2009; Masset et al.,
2010). Setting the initial pH dictates a delicate balance between obtaining optimum
conversion efficiency, and acquiring the fastest rate of hydrogen production. A pH value
outside of the acceptable range can inhibit hydrogen production by altering bacteria’s
metabolism or cause a microbial population shift (mixed inoculum culture) bringing about a
termination in hydrogen production and as such, reliable pH control is crucial.
A study with an initial pH of 5.5 has the highest hydrogen production rate of 2.90
mmolH2/d, at 90 gTS/L, using food waste from cafeteria as substrate (Carlos, 2012). Using
sugar cane bagasse hydrolysate, the optimum pH for hydrogen production was found to be
42
5.5 at a rate of 1611 mL H2/L/day (Sakchai et al., 2008). Generally, it has been shown that
initial pH has a significant effect on both the yield and rate of hydrogen production.
2.9.4 Substrate
In the quest to know which organic substrate will yield more hydrogen, many research have
been carried out. Mostly used substrates are glucose, sucrose and starch. It has been
demonstrated that in an appropriate range, increasing the amount of substrate could
enhance the hydrogen-producing bacteria’s ability to produce hydrogen during fermentative
hydrogen production. Just like the temperature and pH, substrate concentrations at much
higher levels could decrease hydrogen production with increasing substrate levels (Baron,
1996; Yasin et al., 2013; Kimia, 2013; Hori et al., 2005). For example, Akutsu et al, (2009)
showed that there was 18 % decrease in hydrogen yield when substrate concentration was
increased from 15 g/l starch to 20 g/l-starch. Furthermore, the study also revealed no
change in hydrogen yield when substrate concentration was increased from 50 g/l to 70 g/l.
2.9.5 Reactor
There are three major reactors used globally for anaerobic fermentation. Such as serum
batch reactors, continuous stirred tank type bioreactor (CSTR) and an up-flow anaerobic
sludge blanket bioreactor (UASB). See plate 2.1 and 2.2
Hariklia et al., (2006) did a study to examine and compare the biological fermentative
production of hydrogen from glucose in a CSTR and an (UASB) at hydraulic retention
times varying from (2–12 h HRT) under mesophilic conditions (350C). It showed the
UASB reactor configuration to be more stable than the CSTR as regards to hydrogen
production, pH, glucose consumption and microbial by-products, such as, volatile fatty
acids, alcohols etc at the tested HRTs.
43
Plate 2.1 Continuous Stirred tank Bioreactor. Source: (Heidrich and Witkowski, 2010)
Plate 2.2 Up-flow sludge blanket bioreactor. Source : (Heidrich and Witkowski, 2010)
Non-woven
filter
Effluent pump
Control system
Biogas
Stirrer Influent pump
Influent
Bioreactor
Pressure Guage
44
Tawfik and El-Qelish (2012) showed that the rate of hydrogen production in the UASB
reactor was significantly higher compared to that of the CSTR at low retention times (19.05
and 8.42 mmole H2/h/l, respectively at 2 h HRT). It also revealed that a higher hydrogen
yield was found at the CSTR reactor at all tested HRT (Hariklia et al., 2006; Tawfik and El-
Qelish, 2012).
Furthermore, it has been demonstrate that cassava and food waste could be ideal substrates
for bio-hydrogen production using a two-step process combining dark fermentation and
photo-fermentation. The average yield of hydrogen was approximately 199 ml H2 g−1
cassava and 220 ml H2 g−1 food waste in dark fermentation (Zong et al., 2009). The average
yield of hydrogen from the effluent of dark fermentation was approximately 611 ml H2 g−1
cassava and 451 ml H2 g−1 food waste in subsequent photo-fermentation. A combination of
the two has a total hydrogen yield of 810 ml H2 g−1 cassava and 671 ml H2 g
−1 food waste
(Zong et al. 2009).
2.9.6 Acclimatization
Acclimatization in its simple form can be defined as the process in which an organism
adjusts to a gradual change in its environment so as to maintain performance across a range
of environmental conditions (Eroğlu., 2006). This could be a change in temperature,
humidity, or pH. In response to these changes, organisms can change the biochemistry of
cell membranes. Specific proteins called heat shock proteins which help the cell maintain
function under extreme stress may also be expressed by organisms. This adjustment ranges
from days to couple of months depending on the environmental condition.
45
It has been observed that acclimatization plays an important role in enhancing bio-hydrogen
production. For example, a comparative evaluation of anaerobic digester sludge (ADS) and
acclimatized anaerobic digester sludge (AADS) for bio-hydrogen production was done by
Nasr et al., (2011), it was found that a maximum hydrogen yield of 19.5 L H2/L and
7.5 L H2/L thin stillage was achieved for the AADS and ADS respectively (Nasr et al.,
2011).
Another study conducted in a Sequential Batch Reactor with a pH of 5, a temperature of
35 °C was done to show the effect of acclimatization with sewage sludge. It was shown that
acidogenic microorganisms which plays a major role in initiating hydrogen production
increased from 0.160 h−1 to 0.125 h−1 during the acclimatization process. However,
facultative microorganisms remained constant during the acclimatization process
(Fernández et al., 2010).
Hydrogen production by anaerobic fermentation bacteria was investigated in a three-
compartment anaerobic baffled reactor (ABR) by Li et al., (2007). The study showed that
H2 yields in the 1st compartment was lowest with the longest acclimatization period. The
2nd and 3rd compartments were found to have higher hydrogen yields but shorter
acclimatization durations (Li et al., 2007).
2.9.7 Metal Ion
It has also been observed that the metal ion present in substrates may inhibit the activity
hydrogen-producing bacteria especially if not in a trace level. It is well known that low
concentrations of heavy metals such as magnesium (Mg), molybdenum (Mo), manganese
(Mn), iron (Fe), and others are necessary for the growth of purple bacteria
46
(Rhodobactersphaeroides). R. sphaeroides produce H2 under reducing conditions upon the
drop in redox potential, which could determine electron transfer within bacterial membrane
and generation of proton motive force (Hakobyanet al., 2012).
Fe, Mo and nickel (Ni) have been shown to be component of several enzymes involved in
H2 metabolism in photosynthetic bacteria such as nitrogenase and membrane-bound uptake
hydrogenase.
It has been shown that Mg2+ aids more in hydrogen production than Fe2+, Cu2+, Zn2+ and
Ca2+(Wang and Wan 2009). It does so by activating almost 10 enzymes including
hexokinase, phosphofructokinase and phosphoglycerate kinase during glycolysis process
(Voet et al., 1999). The key enzyme for hydrogen production is hydrogenase which requires
ferrodoxin formed from Iron. Thus, iron is an essential element in hydrogen production
process (Nicolet et al., 2002).
However, Zhao et al., (2012) reported that the effects of metal ions on H2 production by C.
beijerinckii RZF-1108 was complicated. They also reported a maximum H2 yield of
1.96 mol H2/mol glucose and production rate of 106.0 ml H2/l medium·h−1 using optimized
culture medium supplemented with 0.2 g/l FeSO4·7H2O and 0.1 g/l MgCl2·6H2O.(Zhao et
al., 2012).
Bao et al, (2013) reported that the addition of Fe2+ and Mg2+ and L-cysteine has a higher H2
yield than the control. Furthermore, the study showed an enhancement of the H2 production
by the sole addition of Fe2+ and L-cysteine was significant (by 105% and 60%,
respectively). The sole addition of Fe2+ to the system had the highest effect with a
47
maximum cumulative H2 production of 1928 mL and H2 yield of 1.94 mol H2/mol glucose
(Bao et al., 2013).
2.10 Gompertz Kinetic Model
Gompertz Kinetic model has been used to describe the progress of hydrogen production.
For example Mu et al., (2007) used it to describe the growth of hydrogen-producing
microorganisms, consumption of substrate and formation of product in this work.
According to Das and Debabrata (2012), it was found that the modified Gompertz kinetic
model was the most suitable to describe the progress of biohydrogen formation process.
The hydrogen production yield and rate is dependent on the experimental conditions such
as temperatures, pH, substrate etc (Mu et al., 2007).
Previous researches have been conducted using this model. Kim et al (2011) showed both
the highest H2 yield of 1.79 mol H2/mol hexose and a production rate of 369.1 ml H2/L/h
were observed at 500C (Kim et al., 2011). Under standard temperature and pressure,
Nazlina et al (2011) used the gompertz model to show that the bio-hydrogen production
potential obtained from fermentation broth at controlled pH values of 5.0, 5.5 and 6.0 were
129 NmL, 444 NmL and 426 NmL, respectively.
Nathao et al., (2013) showed that the highest rate of hydrogen production to be at food 17.9
± 2.7 (mL/h) at food to microorganism ratio of 7.5 (Nathao et al., 2013). Tawfik and El-
Qelish (2012) found that H2 production remained at the same level of 5.3 ± 1.04 L H2/d at
increasing the organic loading rate from 36 to 47 g CODtotal/L d. Under a controlled
48
fermentation pH of 5.5, Hydrogen production rate and yield were about 108 mL/L·h and
128 mL/g CODdegraded respectively (Jong et al., 2008)
2.11 Food Waste
In order to assess how feasible it is to use food waste as a means of feeding anaerobes for
bio-hydrogen production, it is necessary to note the unique potentials.
2.11.1 Potential Environmental Benefits
Using Malaysian scenario, where about 50 % of 33,000 tonnes of MSW produced per day
is food waste (Agamuthu, 2014). Food waste therefore is the largest component of the
Malaysian MSW stream. It will imply that about 16,500 tonnes of food waste goes to the
landfill daily. Thus food waste has become a problem in Malaysia and as such, diverting
this organic component of MSW can serve to greatly reduce landfill loading rates.
Furthermore, this diversion has a high potential of greatly expanding the service life of
landfill.
As food waste decomposes in landfills, it is typically degraded into both CO2 and CH4 gas
and emitted into the atmosphere. Sanitary landfills have gas collection systems to control
these emissions while non-sanitary landfills do not. The ability to capture and collect CH4
gas produced from food waste decomposition provides a significant means of reducing our
overall GHG emissions. However, any technology that will reduce this CO2 and CH4
emission will be saving the environment a great deal of harm (IPCC, 2007).
Furthermore, from a purely space conservation standpoint, it makes sense to prevent the
transportation of food waste to landfills since a significant portion of the MSW stream in
Malaysia is food waste. Siting and operating landfills is a large and complex undertaking,
49
therefore diverting any portion of it the refuse being sent to them will not only increase
their lifespan but will also reduce those problems associated with the decay of the organic
components disposed of, including odors and unwanted pest attraction, it will also reduce
the cost of leachate treatment (Abdul Rahman, 2013).
2.11.2 Financial Considerations
There are other opportunities which will compete with food waste anaerobic digestion (AD)
as recycling options. These include using food wastes as soil amendment through
composting or using food waste as an animal feed. Economically speaking, the AD of food
waste may not be the most preferred option financially for its ultimate food waste disposal.
For example, in the United States, Disney World converts a great portion of its food waste
into animal feed, and the product has even been approved for human consumption by the
United States Department of Agriculture (Jaworski, 2007; Smith, 2010). Nevertheless, in
constructing any AD plant, some factors are taken into consideration. These factors include
space requirements of the facility, water demand, quality and quantity of wastewater
discharged, the quality and quantity of the digestate residual, electricity use and electricity
production and the local biogas markets (Rajendran et al., 2012).
Johari et al.,(2012) estimated that based on 8.2 million tonnes MSW generated in
Peninsular Malaysia in 2010, about 310,220 tonnes per year of CH4 will be emitted (Johari
et al. 2012). This was further estimated to generate about 1.9 billion kWh of electricity per
year worth over RM 570 million (US$ 190 million). Furthermore, about
6,514,620 tonnes year−1 of CO2 will be reduced which is equivalent to carbon credit of over
RM 257 million (US$ 85 million). Converting waste to energy could be economically
viable, depending on factors such as cost of production etc.Factors such as acceptable rates
50
of revenue from carbon credits, sales of renewable energy back to local power utilities or
private purchasers, and tax incentives will determine the financial success of any food
waste digestion enterprise (Lee and Chung, 2010). Organizations like the California
Climate Action Registry (CCAR) serve as an exchange for carbon credits. A protocol was
listed in 2009 for the digestion of organic waste which would also apply to an AD facility
for food waste which attempts to earn revenue through carbon credits (Chum et al., 2011).
Companies who wish to offset their GHG (GHG) emissions will have to be certified by this
organization before buying carbon credits. There are often set rates (usually on a kilowatt-
hour (kWh) basis) by different utility companies at which they are willing to purchase
renewably produced electricity. There is also need for different restaurant and food service
industries to process and separate their waste before disposal. Without this source
separation, additional operational costs will be incurred in AD of food waste in trying to
separate this waste. Based on economic evaluation, two-phase hydrogen and CH4
fermentation was found to have a greater potential for recovering energy than CH4-only
fermentation (Lee and Chung, 2010).
Hydrogen production technology will reduce the cost of maintaining a landfill because the
waste will have little organic in it after diversion. It will also reduce CH4 emission into the
atmosphere. This will in turn reduce global warming and its adverse effect. It is therefore
necessary that studies are conducted on how to commercialize hydrogen production.
The current study was conducted to increase the knowledge base on the conditions needed
for hydrogen production from food waste.
51
CHAPTER 3
MATERIALS AND METHODS
3.1 Food Waste Preparation
The food waste substrates were collected from the University of Malaya cafes. It was
further separated manually into the different components to remove bones, papers, tissues,
plastics etc (Plate 3.1). A blender (super blender, model PB – 326) was used to grind the
separated food waste in the laboratory.
The grinding was to increase the surface area which speeds up the rate of reaction and
enhance microbial activities. It was then sealed in sterile plastic bags and stored in the
freezer at 4oC prior to use. The food waste and the anaerobic sewage sludge were both
thawed before they were used for the experiment.
3.2 Sludge Preparation
Wet anaerobic sewage sludge used as seed sludge in this study was obtained from an
anaerobic digester in Pantai Dalam sewage treatment plant, Kuala Lumpur, Malaysia. After
collection, the sludge was transported to the laboratory and stored in a refrigerator prior to
use for experiments at 4oC. Before the experimental set up, the anaerobic sewage sludge
was thawed to room temperature. It was sieved with 2 mm sieve to remove stones (Chyi-
How et al., 2010). It was then pre-heated at 80oC for 15 minutes. This was to inhibit the
bioactivity of methane forming bacteria and other pathogenic microbes and also to promote
the growth of hydrogen producing bacteria.
52
Plate 3.1: Food waste Collection and Separation
3.3 Alkalinity Determination of Sewage Sludge
Dry Na2CO3 (2.5 ± 0.2 g) was weighed out using a weighing balance. This was transferred
to a 1-L volumetric flask. The flask was filled to the mark with distilled water. The dry
Na2CO3 dissolved in the water forming a standard solution (0.05N).
Standard sulfuric acid 0.1N was prepared and standardize against 40.00 mL 0.05 N Na2CO3
solution, with about 60 mL water, in a beaker by titrating potentiometrically to pH ofabout
5. After titration, the electrodes were lifted out and rinsed into the same beaker, then the
titrate was boiled gently for 3 to 5 min under awatch glass cover. It was further cooled to
room temperature. The normality was calculated.
53
3.4 Volatile fatty acids in Sewage Sludge
Volatile fatty acids (acetic acid, propionic acid, n-butyric acid, isobutyric, valeric acid, iso-
valeric acid) were quantified using a Clarus 500 Gas Chromatography (PerkinElmer®). The
measurement follows the method of Kraemer and Bagley (2008). The oven temperature of
the headspace sampler was set to 85°C. The sample vials went through six steps:
equilibration (about 1 minute), thermostatting (30 min), pressurization (1.5 min), injection
(less than 1 min), withdrawal (less than 1 min) and venting (less than 1 min). The gas
sample was transferred to the Gas Chromatography (GC) by transfer line (105°C), and then
analyzed by GC with a Zebron free fatty acid phase (FFAP) column (30 mm×0.32
mm×0.25 μm) and flame ionization detector (FID). The oven temperature program of GC
started at 45°C for 1.8 minutes, and then ramped to 140°C at 45°C/min, was kept at 140°C
for 2 minutes and finally ramped at 10°C/min to 166°C. The temperature of the FID was
250°C. The gas flow rate of air (Zero Grade) was 450 ml/min, the gas flow rate of H2 was
45mL/min and the gas flow rate of N2 was 2 ml/min. For volatile fatty acids, the retention
times were: 4.619 minutes for acetic acid, 4.98 minutes for propionic acid, 5.462 minutes
for n-butyric acid, 5.06 minutes for isobutyric acid, 6.2 minutes for valeric acid, and 5.67
minutes for isovaleric acid.
3.5 Ammonical Nitrogen in Sewage Sludge
Ammonia concentration was measured by using Method 10031 (Salicylate method) from
the HACH company. Each sample was analyzed in triplicate. Liquid samples were filtered
through 0.45 μm membrane filter (Millipore Express® PLS 0.45μm, 25mm in diameter),
and the filtrate was used in the ammonia measurement. Appropriate dilution with distilled
54
water was conducted to get the measured values within the detection range (0.4-50.0 mg/L
NH3-N).
3.6 Total Suspended Solids (TSS) of Sewage Sludge
A well-mixed sewage sludge was filtered through a weighed standard glass-fiber filter and
the residue retained on the filter was dried to a constant weight at 103 to 105°C. The
increase in weight of the filter represents the total suspended solids. The measurement of
TSS followed Method 2540 D in Standard Methods (APHA, 2005).
3.7 Batch Fermentation
3.7.1 Acclimatization of food waste with Sewage Sludge
Acclimatization was done by mixing 100g of food wastes substrates with 100 mL thawed
anaerobic sewage sludge using a sterile 250 mL conical flask. The conical flask was
covered with aluminum foil (Plate 3.2) and then transferred into an incubator (Memmert
854 Schwabach W- Germany) for 31 days at 370C. 250 mL serum bottle used as the
fermenter was washed clean, sealed with an aluminum foil, and then autoclaved to sterilize
the medium. Using a measuring cylinder (150 mL), 30 mL of wet acclimatized food waste
were then inoculated into the sterile serum bottle (sterilized using Hirayama HVE – 50
autoclave). 8g of each blended food waste substrate was weighed out using an electronic
weighing balance (mark Bel 500, capacity 500,000g) with the weight of a crucible and
added to the batch reactor. The crucible was weighed dry and the weight was noted. The
electronic weighing balance was calibrated before the individual weighing out of 8g was
made. 50 mL of anaerobic sewage sludge heated (pre-treatment) at 800C for 15 minutes
was added to the mixture. The working volume was brought to 150 mL by adding distilled
water. The initial pH was corrected to 4.0, 5.5 or 6.0 using 1N sodium hydroxide (NaOH)
55
and 1N sulphuric acid (H2SO4). The pH meter (model: EL 20, mettle-toledo AG 8603
Schwerzenbach Switzerland) was used to measure this pH. The correction was done by first
knowing the pH of the samples, and then NaOH or H2SO4 were added in drops
simultaneously. The mixture was then stirred until the desired pH was obtained. The batch
reactors were then corked with a septa and an aluminum seal using a crimper in order to
make the batch reactors air tight. To maintain an anaerobic condition the headspace of the
batch reactors were filled with pure N2 gas. Mixing was done manually twice a day. Each
experimental condition was carried out in triplicates. The batch reactors were then placed in
a water bath (model: baird and Tatlock, made in England) and monitored at temperature
range of 270C, 350C and 550C.
Plate 3.2: Acclimatized Food Waste Substrates
3.7.2 Non Acclimatization
Here, 8g of the blended food waste substrate was mixed with 50 mL of thawed anaerobic
sewage sludge without adding any incubated mixture. The mixture was added into a 250
56
mL serum bottle (Plate 3.3). The working volume was adjusted to 150 mL using distilled
water and the initial pH was corrected to pH values of 4.0, 5.5 and 6.0. The sludge was pre-
heated in a 500 mL volumetric flask at 80oC for 15mins before mixing it with the food
waste substrates. The head space of the bottle was also filled with N2 gas. This is to make
the medium completely anaerobic.
Plate 3.3 Food Waste in a 250 mL serum Bottle
After conditioning, the batch bottles were then placed in a water bath at 27, 35, and 55 ±
2oC till the end of the experiment. Attached to a transfusion tube was a transfusion needle
at one end. The other end was bored into rubber cork at the mouth of a conical flask full of
water. This same open end was made to touch the bottom of the conical flask. This was to
57
ensure proper water displacement. The rubber cork was further made air tight using a
sealant. The conical flask also has an outlet transfusion tube which also touches its bottom.
This outlet transfusion tube conveys displaced water out of the conical flask. The displaced
water was collected in another conical flask and measured using a measuring cylinder as
shown in Fig 3.1. The amount of biogas produced was measured by the amount of water
displaced as shown in plates3.4 and 3.5. Thus, the amount of water displaced was used to
calculate biogas production and the amount of hydrogen gas produced was detected by the
gas chromatography (GC, shimadzu 8A).
Figure 3.1 Schematic Diagram of Biogas Production
58
Plate 3.4 Biogas Production and water displacement
Plate 3.5 Level of Water displaced for Biogas Measurement
59
3.8 Effect of Metal Ions on Bio-hydrogen production
Furthermore, a study to know the effect of heavy metal ions on bio-hydrogen production
from food waste substrates was conducted. This was because it is possible that batteries
(containing lead (Pb)) could be found in the MSW stream.
8g of mixed food waste was weighed with an electronic weighing balance (mark Bel 500,
capacity 500,000g) and added into a 250 mL serum bottle (batch reactor). Using the
weighing balance, 5mg, 10mg and 15mg lead (Pb) were weighed out in a crucible and
diluted with 1000 mL of deionized water. This mixture was carefully transferred into the
serum bottles. 50 mL of acclimatized anaerobic sewage sludge was then added using a
measuring cylinder to the reactor. Then distilled water was used to get a working volume of
150 mL. The pH was then corrected to 5.5 using 1N NaOH or 1N H2SO4. As usual, the
reactor was purged with N2 gas and put in a water bath at 350C. A control was set up
alongside having no metallic ions in it. These experiments were conducted in triplicates to
minimize experimental error.
3.9 Column Experiment
A column of 30 cm having only one outlet when sealed with a sealant was used to
investigate the effect of a slightly bigger reactor on bio-hydrogen production. The column
has two ends, the bottom was permanently sealed while the upper end was open for food
waste substrate addition before sealing was done. A tap was tightly fitted just before the
open end for biogas sampling and analysis (Fig 3.2). 24g of the food waste was added into
the column, 5 mg, 10 mg and 15 mg of lead was weighed out with an electronic weighing
balance. It was further diluted with 1000 mLs of deionized water and added into the column
60
from the open end. The column size was 3 times the bottle size, therefore for easy
comparison, the amount of substrates used were trice that used in the bottle experiments.
150 mL of heat treated anaerobic sewage sludge was then added to the mixture in the
column, 150 mL Acclimatized anaerobic sewage sludge was also added, then distilled
water was further added to get the working volume of 750 mL. The reactor was shaked
vigorously and the pH corrected to 5.5 using 1N NaOH or 1N H2SO4. The air in the reactor
was sucked out using a vacuum machine. N2 was used to purge the system to make it
anaerobic. The set up was then put in an incubator at 35oC ± 2oC. Daily measurement was
conducted to measure the amount of biogas produced through water displacement. This was
done by carefully placing a transfusion tube over the tap on the column. Then the free end
of this transfusion tube was connected through a rubber cork into a conical flask full of
water. The conical flask also has an outlet transfusion tube. This tube conveys the displaced
water into an empty conical flask where the water was collected and measured using a
measuring cylinder as shown in Fig 3.2. The amount of biogas produced equals the amount
of water displaced.
Figure 3.2 Schematic Diagram of Column Experiment on Biogas production
61
3.10 Moisture Content of Food Waste
The mass of the substrates were determined using an electronic weighing balance. In order
to determine the characteristics of the food waste, a porcelain dish was weighed dry and the
weight noted, then about 20 g of each substrate was added to it and the total weight was
also noted. The dish containing the wet sample was then put in a desiccator for a day to
avoid absorbing extra moisture from the environment. It was then put into an oven at a
temperature of 1050C for 24 hours. The dry samples were then brought out from the oven
and weighed; the difference in weight was recorded as the moisture content of each sample.
3.11 Biogas Analysis
The volume of biogas production in each batch reactor was measured and recorded through
the water displacement method. Biogas sampling began as soon as biogas was produced in
the reactor. One mL of the biogas was taken with the 1mL gas tight syringe (model 1MR –
GT, M04 – C3985) from the batch reactors. It was then injected into a gas chromatography
(GC Shimadzu 8A) with thermal conductivity detector to analyze the H2 content. Helium
gas was used as the carrier gas at a flow rate of 60 mL/min. The injector, detector and
column operated at 160oC, 130oC and 130oC respectively (Plate 3.6). Pure hydrogen gas
was used for calibration.
The hydrogen production potential and the rate of production were analyzed using the
modified Gompertz kinetic model (Zwietering et al., 1990).
𝐻(𝑡) = 𝑃 . exp[−𝑒𝑥𝑝 { 𝑅𝑚 .𝑒(ƛ−𝑡)
𝑃 + 1}]………………….(6)
62
Where H (t) is cumulative hydrogen production (mL), P is hydrogen production potential
(mL), Rm is maximum hydrogen production rate (mL/d), e = 2.71828, ƛ is the lag phase (d)
and t is the time (d).
Plate 3.6: Gas chromatography (GC) used for biogas analysis.
3.12 Statistical Analysis
Statistical analysis were carried out using Microsoft excel software because the data to be
analyzed was not very large. To compare the amount of gas produced from each substrate,
a one way single factor ANOVA was used. One way single factor ANOVA was also used
to compare the mean values in all four substrates (rice versus fish, rice versus vegetable,
rice versus mixed, mixed versus fish, mixed versus vegetable, fish versus vegetable). This
was to determine their significance. The level of statistical significance was set at 5% Post-
hoc analysis and 95% confidence level.
63
The Kuskal Wallis non parametric test was used to compare the amount of cumulative
biogas production produced by all four substrates between the acclimatized and non-
acclimatized food waste substrate. The level of statistical significance was set at 5% Post-
hoc analysis and 95% confidence level.
One Way factor ANOVA was also used to compare the amount of biogas and hydrogen
produced by the food waste containing metallic ion (Pb) at different concentrations.
Mean values were used in graphical representations.
64
CHAPTER 4
RESULTS AND DISCUSSION
This chapter discusses the effect of temperature and pH on bio-hydrogen production using
food waste substrates. Gompertz kinetic model was used to determine the rates and
potentials of hydrogen production. The model also identifies the substrate that has the
highest H2 production rate.
4.1 Composition of Food Waste
Composition of kitchen waste used in this study is given in Table 4.1. The notable
characteristics of the food waste were their high moisture content (70% - 80%). This
definitely forms leachate when dumped in a landfill. The food waste substrates used in this
study were obtained from different batches collected at different times. The composition of
the different batches showed that the standard deviation was low. TS and TSS represented
the solid content in food waste substrates. The large amount of TS and TSS might be due to
the varieties of leftover raw and cooked food, as well as, the peels of fruits and vegetables.
The pH became acidic probably because upon dark fermentative transformation, hydration
of glucose molecule elucidates a simultaneous formation of acetic acid and hydrogen
(Yasin et al., 2013).
This result is similar to previous studies by Han and Shin (2004), Zhang and Wang (2005),
where the moisture content of food waste used for biogas production was 70 % and 79 %
respectively. However, the current study has higher TS and lower pH when compared with
65
that of Han and Shin (2004). This might be due to the different sources of food waste
collection(Ruihong, 2007).
Table 4.1 Characteristics of Food Waste used
Food Waste
Substrates
pH
(initial)
pH (final) Total
Solid(TS)
(g/l)
Total
Suspended
Solid(TSS)
(g/l)
Moisture
(%)
Rice 5.9±0.22 4.3±1.22 100.50±0.52 70.42 ± 1.22 80 ± 2.25
Vegetable 5.2±0.24 4.5±0.34 102.04±0.32 86.32 ± 2.34 72 ± 1.76
Fish 5.0±0.21 4.0±0.42 98.32 ± 0.72 87.42 ± 2.50 70 ± 1.64
Mixed 5.2±0.22 4.2±1.36 110.21±0.68 88.51 ± 1.25 70 ± 2.34
ASS means Anaerobic Sewage Sludge
4.1.1 Characteristics of Anaerobic Sewage
The sewage sludge characteristics are subject to change depending on its nature and
treatment of sewage, which affects the properties of these wastes. The characteristics of the
sewage used in this study are given in Table 4.2. The pH of 7.57 can be said to be neutral.
Thus, the sludge remains in the methane digestion stage (Kijo-Klecckzkowska et al., 2012).
The low alkalinity of 286 mg/L shows that the amount of dissolved alkaline compounds in
the liquid sludge is low. The Low Volatile Fatty Acids and Ammonical Nitrogen all points
to the fact that the sludge was well digested. This might be because it was collected from
anaerobic sludge digester tank (Kijo-Klecckzkowska et al., 2012).
66
The characteristics of the sludge in the current studies agree with the characteristics of the
well digested sludge as classified in previous studies (Kijo-Klecckzkowska et al., 2012;
Heidrich, 2004; Heidrich, and Witkowski, 2010). Nevertheless, the alkalinity of the sludge
used in the current study falls under the secondary sludge. This might be because the
moisture content (50 %) of the sludge used in the current study falls into secondary sludge
characteristics.
Table 4.2 Characteristics of the Anaerobic Sewage Sludge used in this study
Test Parameter Result
Ammonical Nitrogen 5.39 mg/L
Alkalinity ( as CaCO3) 286 mg/L
Volatile fatty acids 120 mg/L
Volatile Suspended Solids 5782 mg/L
Organic Carbon 1.75%
pH 7.57
Moisture 50 %
4.2 EFFECT OF TEMPERATURE
4.2.1 Effect of Temperature on Cumulative Biogas and H2 Production Using Rice
Waste as Substrate
When the substrate was subjected to a temperature of 350C, biogas production was recorded
on day zero as opposed to H2 gas which commenced on day one (Figure 4.1). This might be
because the temperature was favorable for H2 producing bacteria to proliferate. There was a
rapid increase in the production of biogas and H2 reaching its peak on the 9th day before
67
stabilizing from the 10th day onward. This could also be because the temperature made
sugar conversion easier for the Hydrogenase which in turn increases H2 production
(Jingwei et al., 2008).
Figure 4.1 Effect of temperature on Cumulative Biogas and H2 Production Using Rice
waste as Substrate
Also, considering biogas and H2 production at other temperatures, it was observed that at
270C and 550C, H2 and biogas production commenced on the 4th day. There was a slow
increase in the H2 production observed for substrates at 270C before reaching its peak on
the 7th day with a H2 yield of 7.76 mL. The long lag period was probably because the
temperature was unfavorable for H2 producing bacteria (Jianlong and Wan, 2009).
0
5
10
15
20
25
30
0
5
10
15
20
25
30
35
0 5 10 15
H2
Con
ten
t (m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Fermentation Days
27°C Cumulative
Biogas Production(mL)
35°C Cumulative
Biogas Production(mL)
55°C Cumulative
Biogas Production(mL)
27°C Hydrogen
35°C Hydrogen
55°C Hydrogen
68
Furthermore, it was observed that the maximum H2 production recorded at 550C was 4.85
mL. This was probably because the H2 producing bacteria survived for a while but were
inhibited by the high temperature. Generally, the optimum temperature for bio-H2
production using rice waste was found to be 350C in this study.
This agrees with previous report by Fang et al., (2006) showing the optimum temperature
for H2 production from rice waste to be 5.5 even though Fang et al., (2006) recorded a
higher maximum H2 yield of 346 mL. This higher yield might be because the substrate used
by Fang et al (2006) was rice slurry which provides an enabling environment for the
microbes. Results in this research was not in agreement with those of Lee et al., (2008) and
Elijah et al., (2009) where the optimum temperature was 550C, which might be because
they used rice husk and as such higher temperature was needed to get the nutrients out
(Elijah et al., 2009).
Moreover it was statistically shown that H2 production from rice waste as substrate was
statistically significant at 370C (P < 0.001) than at 270C and 550C. The same was the case
when statistical analysis was conducted for cumulative biogas production.
4.2.2 Effect of Temperature on Cumulative H2 production and H2 Content Using
Fish waste as Substrate
H2 and biogas production commenced on the 6th day when the fish waste were subjected to
a temperature of 270C (Fig 4.2). This was probably because of unfavorable temperature
coupled with the acidic content of fish waste. A slight increase in H2 production was
69
observed from the 7th day before reaching its peak on the 9th day after which it decreased to
zero on the 10th day.
Figure 4.2 Effect of Cumulative Biogas production and H2 content Using Fish waste as
Substrate
At 350C, biogas and H2 production commenced at day one. A rapid increase was observed
until it reached its peak on day 5, then a sudden fall in H2 production was observed after the
5th day. The rapid increase and fall could be because temperature 350C was favorable at the
start but the production of carbon-dioxide made the system more acidic that the medium
became harsh for the survival of hydrogenase enzyme (Nazlina et al., 2009). For 550C,
H2and biogas production commenced on the 1st day. We also observed maximum H2
0
10
20
30
40
50
60
70
80
90
100
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15
H2
Con
ten
t (m
L)
Cu
mu
lati
ve
Bio
gas
pro
du
ctio
n (
mL
)
Fermentation Days
27°C Cumulative
Biogas Production(mL)
35°C Cumulative
Biogas Production(mL)
55°C Cumulative
Biogas Production(mL)
27°C Hydrogen
35°C Hydrogen
55°C Hydrogen
70
production of 63.72 mL which also decreased gradually until no H2 gas was produced. This
might also be due to the high carbon dioxide content observed in the fish which helps to
increase the acidic content of the mixture (0-thong et al., 2007). H2 and biogas production
commenced after 6 days when fish waste substrate was subjected to 270C which lasted for
just 3 days. This might be because the temperature was low and as such hydrogen
producing bacteria had tough time adjusting with the temperature (Nazlina et al., 2009).
The 3 days production period was probably due to the carbon-dioxide produced by fish
which makes the system acidic, thus, inhibiting hydrogenase(O-Thong et al., 2007;
Okamoto, 2000).
Generally, the optimum temperature for H2 production using fish waste as substrate was
350C. The low yield in fish waste could also be attributed to the amino acid which is the
catalytic end product of protein (Michael, 2006).
The amount of H2 produced by fish waste at 350C was statistically significant than the
amount produced at 270C and 550C (P < 0.05). Likewise, the amount of biogas produced at
350C was statistically significant than the amount produced at 270C and 550C (P < 0.001).
This agrees with previous reports where the optimum temperature for H2 production using
protein substrate was 350C (Zhu, 2011; Keigo and Shigeharu, 2006; Shin et al., 2004).
71
4.2.3 Effect of Temperature on Cumulative Biogas production and H2 Content Using
Vegetable Waste as Substrate
It was observed that no gas production was recorded when vegetable waste substrate was
subjected to 270C and 550C (Figure 4.3). This might be because at 270C, the lactic acid
fermentation bacteria which operate better at this temperature range liberated ascorbic acid
which is richly present in vegetables. This liberation therefore makes the medium more
acidic and thus unsuitable for H2 producing bacteria as shown in Table 4.1 (Leon, 2011).
According to Okamoto (2000), H2 producing bacteria are more active at temperatures 35 -
40; therefore 550C might be too high for the bacteria to act on vegetable waste substrate
(Okamoto, 2000).
Figure 4.3 Effect of Temperature on Cumulative and H2 Production Using Vegetable Waste
as Substrates
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
0 5 10 15
H2
Con
ten
t (m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Fermentation Days
27°C Cumulative Biogas
Production(mL)
27°C Hydrogen
35°C Cumulative Biogas
Production(mL)
55°C Cumulative Biogas
Production(mL)
35°C Hydrogen
55°C Hydrogen
72
Nevertheless, biogas and H2 production commenced when the vegetable waste as substrate
was subjected to a temperature of 350C. On day one, gas production was recorded. A rapid
increase in H2 production was observed from the second day until a maximum of 92 mL
was reached on the 4th day. The subsequent days showed a gradual decrease in H2
production until it stabilized from the sixth day onward. This was probably because the
temperature favored H2 producing bacteria. It could also be because most plants that grows
in temperate regions like Malaysia contains indigenous bacteria which do well at 35oC
(Merrill, 2010).
This result is different with previous reports by Krishnan et al. (2007) and Chu et al.
(2008). They recorded gas production at 550C. This was probably because only one
vegetable waste type was used in these studies compared to more than one that was used in
the present study. Nevertheless, this result agrees with Okamoto (2000) who reported 350C
as the optimum temperature for bio-H2 production from vegetable waste substrate.
The amount of H2 produced by vegetable at 350C was statistically significant than the
amount produced at 270C (P < 0.001) and 550C (P < 0.001). This is because no gas
production was observed when vegetable substrate was used for bio-H2 production at 270C
and 550C.
4.2.4 Effect of temperature on Cumulative Biogas Production and H2 Content Using
Mixed Food Waste as Substrate
Cumulative biogas and H2 production of mixed food waste substrate, at 270C and 350C,
commenced on the 5th day (Figure 4.4). There was a slow but steady increase in the
production of biogas and H2 at 270C until it reached its peak on the 8th day. However, on
73
the 9th day, no H2 production was observed. Furthermore, a rapid increase in H2 production
was recorded at 350C on the 5th day until a maximum cumulative H2 production of 108.9
mL was recorded on the 7th day before dropping sharply to zero on the 8th day. No biogas or
H2 production was recorded for mixed waste substrates at 550C.
The five days lag period observed at 350C could be because this waste has rice, a source of
carbohydrate, fish, a source of protein and vegetable, a source of vitamins, hence it will
take a longer time for these three to be acclimated. The higher cumulative biogas and H2
yield recorded at 350C could be because H2 producing bacteria were able to maintain the
pH of 5.5 at 350C and as such more biogas and hydrogen were produced (Nazlina et al.,
2011).
Figure 4.4 Effect of temperature on cumulative biogas production and H2 Content Using
Mixed Food waste as Substrate
0
20
40
60
80
100
120
0
20
40
60
80
100
120
140
160
0 5 10 15
H2
Co
nte
nt
(mL
)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Days
27°C Cumulative
Biogas
Production(mL)
35°C Cumulative
Biogas
Production(mL)
55°C Cumulative
Biogas
Production(mL)
27°C Hydrogen
35°C Hydrogen
55°C Hydrogen
74
This result agrees with previous reports by Xiao et al., (2013) having optimum temperature
of 370C. It also agrees with that of Chen et al., (2006) having the maximum H2 yield of 101
mL. This might be because anaerobic sewage sludge from anaerobic digester was used in
both studies. Similarly, previous report by Pan et al. (2008) recorded H2 production at 500C.
This might be because of the temperature difference of 50C which could be harmful to H2
producing bacteria (Lin et al., 2008). Nevertheless, a report by Shimizu (2008) agrees with
this study, recording no gas production at 55oC.
Statistically, there was no significant difference in the amount of H2 gas produced at the
two temperature of 27oC and 35oC, where gas production was recorded using mixed food
waste as substrate (P = 0.25). Nevertheless, the amount of biogas produced by mixed food
waste at 350C was statistically significant than the amount produced at 270C (P < 0.05) and
550C (P < 0.01). Thus, we could say that for an enhanced bio-H2 production using mixed
food waste substrate, room temperature ranges are favorable.
Vegetable waste produced no gas when subjected to experimental condition of 27oCand
55oC (Table 4.3). However, rice and fish waste produced gases at all the experimental
conditions of 27oC, 35oC and 55oC. Furthermore, it was observed that all the waste
substrates used were able to produce biogas and hydrogen gas at 35oC. It can be observed
that mixed food waste substrate also recorded the highest cumulative hydrogen production
while fish waste recorded the highest cumulative biogas production at 35oC. It can be
observed also that throughout the food waste substrates, the biogas and hydrogen produced
was highest when they were subjected to a temperature of 35oC. Thus, we can say that the
optimum temperature for bio-hydrogen production from food waste was found to be 35oC
in this study.
75
This is in agreement with number of studies carried out previously (Kim et al., 2004, Jo et
al., 2007, Zhu et al., 2011, Munoz -Páezet al., 2012). The biogas and hydrogen yield tends
to vary across these studies. This is probably because of the differences in the types of
substrates used for bio-hydrogen production.
Table 4.3 The maximum cumulative biogas and hydrogen production from different
temperatures
FWS 27oC 35oC 55oC
MCB
(mL)
MCH
(mL)
MCB
(mL)
MCH
(mL)
MCB
(mL)
MCH
(mL)
Rice 8.00± 1.25 7.76±0.35 31.00±1.22 26.97±0.76 5.00±2.23 4.85±1.87
Fish 18.00±
2.27
7.56 ± 1.18 184.00±3.46 89.70 ± 1.25 124.00±1.23 63.74
±2.23
Vegetable Nil Nil 52.00±2.25 42.00±1.76 Nil Nil
Mixed
Waste
26.00±2.45 25.22±0.76 137.00±3.20 108.90±1.42 Nil Nil
Number of replicates = 3. FWS = Food Waste Substrates, MCB = maximum cumulative
biogas, MCH = maximum cumulative hydrogen, Nil = no gas production was recorded.
4.3 Effect of pH at 350C on Bio-hydrogen Production Using Food Waste as
Substrates
It is very important that proper pH is provided when fermenting food waste for bio-H2
production purposes (Wang and Wan, 2009). Optimum pH can enhance bio-H2 production.
This is because pH has effects on the H2 production metabolic pathways (Kimet al., 2011).
pH can affect the H2 production yield, biogas content, organic acids produced and
76
H2production rate. Four different food waste substrates were used; Rice, Fish, vegetable
and mixed for this study.
4.3.1 Effect of pH on Cumulative biogas Production and H2 Content of Biogas from
Rice Waste
Figure 4.5 shows the effect of pH on Bio-H2 production using rice waste substrate. It can be
observed that when the substrate was subjected to pH of 5.5, cumulative biogas production
was recorded on day zero while H2 gas production commenced on day one. There was a
rapid increase in the production of H2 and biogas reaching its peak on the seventh day,
before it gradually decreased.
Figure 4.5 Effect of pH on Cumulative Biogas and H2 Production using Rice Waste as
Substrate
0
5
10
15
20
25
30
0
5
10
15
20
25
30
35
0 5 10 15
H2
Con
ten
t(m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n(m
L)
Fermentation Days
Rice pH 4 Cumulative
Biogas Production(mL)
Rice pH 5.5 Cumulative
Biogas Production(mL)
Rice pH 6.5 Cumulative
Biogas Production(mL)
Rice pH 4 Hydrogen
Rice pH 5.5 Hydrogen
Rice pH 6.5 Hydrogen
77
Also, looking at the amount of gas produced at different pH values, it was observed that, at
pH 5.5, rice waste produced the highest amount of H2 gas (26.97 mL). This was probably
because the H2 producing bacteria are more active at an initial pH of 5.5 as was previously
reported (Keigo and Shigeharu, 2006). On the other hand, Fang et al., (2006) in a similar
study using a different substrate as waste (rice slurry) observed that the production of H2
was highest at pH 4.5. The current study did not incorporate rice slurry and as such was
unable to draw comparison between their studies (Fang et al., 2006) and the present study.
At pH 6.5, there was a delay of about 4 days in the production of H2 and cumulative biogas
at pH 5.5. This delay could be attributed to the time taken for volatile fatty acids to be
converted to H2 at pH 6.5 as was observed by Jayalakshmi et al., (2007). However, despite
the lag in the production of H2 and cumulative gas, a rapid increase in H2 production was
observed reaching a stable value on the 8th day, yielding maximum H2 gas of 6.76 mL. This
quantity of H2 gas was much lower than 32.9 mL produced by rice waste in Nazlina et al
study (2011) in which unlike the present study, the pH was controlled throughout the study
period. There was a delay of about 5 days before production of H2 gas commenced when
the substrate was treated at pH 4. However, the gas production also increased rapidly
afterwards up till the eighth day when a maximum yield of 3.9 mL was observed. In a
previous study (Masset etal., 2010), it was observed that rice waste produced maximum H2
cumulative yield of 45 mL when the experiment was conducted at pH 4.4. This amount of
H2 gas produced was considerably higher than that reported in the present study mostly
because of the different pretreatment methods used in their study and the different
carbohydrate sources employed. It is therefore very important that proper pH be selected so
that H2 production can be maximized. The results presented here reveals that, a pH of 5.5 is
the optimum pH required to enhance H2 production when rice waste is used as a substrate.
78
4.3.2 Effect of pH on Cumulative Biogas and H2 Production of Using Fish Waste as
Substrate
Production of H2 commenced on day one for both pH 5.5 and 6.5, when fish substrate was
used (Fig 4.6). At pH 5.5 there was a rapid increase in production of H2 reaching a
maximum of 88.4 mL on the fifth day, before the production dropped sharply to zero on
day six. In contrast, the increase in cumulative gas production followed a curvilinear
pattern while stabilizing at a maximum production of 184 mL from the ninth day to 12th
day. The sudden drop in H2 gas production observed at this pH state of the fish waste could
be because of the drop in pH as observed at the end of the experiment (Table 4.1). For this
reason, after the 5th day, the H2 producing bacteria were inhibited as such H2 production
was also inhibited (Shimizu, 2008).
Figure 4.6 Effect of pH on Cumulative Biogas and H2 Production of Using Fish waste as
substrate.
0
10
20
30
40
50
60
70
80
90
100
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15
H2
Con
ten
t (m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Fermentation Days
Fish pH 4 Cumulative
Biogas Production(mL)
Fish pH 5.5 Cumulative
Biogas Production(mL)
Fish pH 6.5 Cumulative
Biogas Production(mL)
Fish pH 4 Hydrogen
Fish pH 5.5 Hydrogen
Fish pH 6.5 Hydrogen
79
On the other hand, at pH 6.5, the production of H2 gas and cumulative biogas increased
gradually reaching a maximum of 32 mL and 65 mL respectively on the 4th day. However,
the subsequent days showed a decrease in the amount of H2 gas produced. This decrease
meant that at day six no H2 was observed in the system. It was observed that cumulative gas
production continued and appeared to have stabilized from the 4th day onward. We also
observed a maximum production of H2 gas (15 mL) on the 5th day, at pH 4, which also
decreased till no H2, was produced on the 8th day. We had also observed that after the
experiment, that across the studied pH ranges, the pH reduced until it became acidic at pH
3.0. Again, this was because of the increased production of carbon dioxide at these low pH
ranges which meant that the system was so acidic that the H2 producing bacteria were
unable to as noted also by Li (2007).
4.3.3 Effect of pH on Cumulative Biogas and H2 Production of Vegetable Waste As
Substrate
Just like rice and fish waste substrates, H2 production was observed first at pH 5.5 on day 1,
which then increased rapidly and reached a peak 45.24 mL at the 4th day and then decreased
to zero (Figure 4.7). The drop in H2 production could be because of the acidic nature of
vegetable and of the individual components of vegetable (Krishnan et al., 2007; Yap,
2013). At pH 4.0, H2 production began on day 4 but the biogas was more of carbon dioxide
than H2 and also dropped after 4 days. pH 4 is acidic therefore when combined with
continuous production of carbon-dioxide, the H2 producing bacteria could not survive the
high acidic medium (Lee et al., 2008; Yap, 2013). The H2 content of the cumulative biogas
was quite small at pH 4. At pH 6.0, no gas production was observed. This could be as a
result of the nearness of the pH to neutrality and possibly the H2 producing bacteria may
not do well above pH 5.5. Nevertheless, research by Lee et al (2008) also revealed a
80
contrast optimum pH of 7.0. This might be because of kitchen waste compost that was
added to the reactor which will have similar microbes as the ones present in the system.
Another previous study by Chyi-How et al. (2010) revealed the optimum pH for bio-H2
production was 6.0. This might be due to the use of preserved fruit soaking solution as
substrate without any additional microbes from sewage sludge or compost.
Figure 4.7 Effects of pH on Cumulative Biogas and H2 Production Using Vegetable Waste
as Substrate
0
5
10
15
20
25
30
35
40
45
50
0
10
20
30
40
50
60
0 5 10 15
H2
Con
ten
t (m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Fermentation Days
pH 4 Cumulative
Biogas Production(mL)
pH 5.5 Cumulative
Biogas Production(mL)
pH 6.5 Cumulative
Biogas Production(mL)
pH 6.5 pH 6.5
Hydrogen
pH 4 Hydrogen
pH 5.5 Hydrogen
81
4.3.4 Effect of pH on Cumulative Biogas Production and H2 Content Using Mixed
Food Waste as Substrate
Substrates subjected to pH of 4.0, caused cumulative biogas production as well as H2 gas
production on the 4th day (Figure 4.8). This was probably because of the acidic nature of
the medium which is not too favorable for the H2 producing bacteria (Jayalakshmi et al.,
2007). There was a slow increase in production of H2 and biogas reaching its peak on the
9th day, before sharply dropping to zero on the 10th day. This could be because the H2
producing bacteria were trying to adjust to the environment but eventually they could not
survive so the H2 production stopped (Masset et al., 2010).
Figure 4.8 Effects of pH on Cumulative Biogas and H2 Production Using Mixed food waste
as Substrate
0
20
40
60
80
100
120
140
0
20
40
60
80
100
120
140
160
0 5 10 15
H2
Con
ten
t(m
L)
Cu
mu
lati
ve
Bio
gas
Pro
du
ctio
n (
mL
)
Fermentation Days
pH 4 Biogas Cumulative
Production(mL)
pH 5.5 Biogas Cumulative
Production(mL)
pH 6.5 Biogas Cumulative
Production(mL)
pH 4 Hydrogen
pH 5.5 Hydrogen
pH 6.5 Hydrogen
82
Also, looking at the amount of gas produced at different pH values, it was observed that, at
pH 6.5, biogas and H2 production commenced together on the 4th day. This was probably
because the pH was close to being neutral. A rapid increase was recorded from the 5th day
before reaching its peak on the 8th day, before it gradually decreased to zero on the 10th day.
This was probably because the pH being slightly acidic still allows H2 producing bacteria to
grow but was also favorable for H2 consuming bacteria which probably inhibited the H2
production (Fang et al., 2006). It was also observed that at pH 5.5 biogas and H2 production
commenced on the 3rd day before increasing slowly on the 4th and 5th day. However, the
subsequent days showed a rapid increase before stabilizing from 8th day onward. The
shorter lag period observed in pH 5.5 might be because the H2 producing bacteria were
favored by pH 5.5 (Shimizu, 2008).
This result was similar with previous reports showing that the optimum pH for H2
production from mixed food waste was ranging from 6.5 (Han and Shin, 2004), 5.6
(Keigoand Shigeharu, 2006), 7.0 (Renet al., 2006) and 6.0. Many of these studies used a
continuous batch reactor rather than the batch reactor as used in the present study and as
such the difference in the reactor sizes may account for the differences in the reported
results. Nevertheless our results agree with those of Atif et al. (2005) and O-Thonget
al.(2007) where the optimum pH for H2 gas production was 5.5 even though palm oil mill
effluent (POME) was used. Another study (Shimizu, 2008) recorded little or no H2
production at pH 5 and 6, using only one bacteria species, while the current study has more
than one bacteria species. It was furthermore shown in a recent study that bio-hydrogen
production stopped as pH dropped below 5 (Xiao et al., 2013).
83
After a period of 12 days, it was observed that pH reduced across the entire food waste
substrates fermentation. This decrease in pH might be due to the organic acids formed
during the fermentation process, which in turn reduced the buffering capacity of the
medium. Such drop in pH is capable of changing the metabolic pathway from a hydrogenic
to a non-Hydrogenic process and can inhibit substrate utilization (Kim et al., 2011). In
addition, a drop in pH was also shown (Keigo and Shigeharu, 2006) to be capable of
directly limiting the production of H2 gas due to the decline in the activity of Hydrogenase
which occurs at excessively low pH.
It can be observed that the maximum cumulative biogas hydrogen production across the
food waste as substrate was highest when the food waste was subjected to pH of 5.5 (Table
4.4). Fish waste substrate recorded the highest maximum cumulative biogas production
(184.00 ± 3.46) mL. Mixed food waste substrate recorded the highest maximum cumulative
hydrogen production (102.00 ± 1.42) mL. As shown in Table 4.4, gas production was not
recorded for vegetable waste substrate at pH of 6.5. Furthermore, the maximum hydrogen
production from vegetable waste at pH 4.0 was 1.1±077 mL.
Fish waste produced more carbon dioxide than hydrogen gas. This may account for its high
amount of cumulative biogas production. Fish waste however, is also a rich source of
protein and ammonia nitrogen, this may also account for its high biogas yield (Michael et
al., 2006; Tomczak-Wandzel and Levilin, 2013). The highest maximum cumulative
hydrogen gas production from mixed food waste substrate could be due to the combined
effect of hydrogenase enzyme found in all the substrates. This effect led to a longer lag phase but
higher maximum cumulative hydrogen yield (Valdez and Varaldo, 2009).
84
Table 4.4 Maximum Cumulative Biogas and Hydrogen Production at Various pH
FWS 4.0 5.5 6.5
MCB (mL) MCH (mL) MCB
(mL)
MCH
(mL)
MCB
(mL)
MCH
(mL)
Rice 4.00± 1.25 2.92±0.25 31.00±1.22 26.97±0.76 7.00±2.23 4.75±1.87
Fish 65.00± 2.27 32.00± 1.18 184.00±
3.46
88.40± 1.25 21.00± 1.23 2.70± 2.23
Vegetable 30.00±1.53 1.1±.077 52.00±2.25 45.24±1.76 Nil Nil
Mixed 37.00±2.45 33.30±0.76 137.00±3.20 102.00±1.42 102±2.54 79.20±2.24
Number of replicates = 3. FWS = Food Waste Substrates, MCB = maximum cumulative
biogas, MCH = maximum cumulative hydrogen, Nil = no gas production was recorded.
4.4 EFFECTS OF ACCLIMATIZATION
Acclimatization refers to a mixture of the substrate with anaerobic sewage sludge which
was allowed to acclimate for a certain period at mesophilic temperature (Dong et al., 2009).
Heat pre-treatment was used to enhance the growth of H2 producing bacteria and inhibit the
methanogens from anaerobic sewage sludge before they were added to the various food
wastes substrates (Chen et al., 2012). This process would encourage additional waste
minimization because two different waste are used (food waste and anaerobic sewage
sludge), thus reducing waste disposal and treatment needs. In order to know if the use of
anaerobic sewage sludge was helpful in the production of H2 by the H2 producing bacteria,
effect of acclimatization was studied and below are the findings on the various food waste
substrates used in this study.
85
4.4.1 Effects of Acclimatization on Cumulative Biogas and H2 Production Using Rice
Waste as Substrate
It was observed that H2 production commenced on the second day as for the acclimatized
rice waste as opposed to the 4th day for non-acclimatized rice waste (Figure 4.9). The
maximum H2 production was recorded on the 10th day (13.6 mL) for non-acclimatized rice
waste and on the 9th (26.97 mL) for the acclimatized rice waste respectively. H2 production
stabilizes from the 11th day for the acclimatized and on the 9th day for the non-acclimatized.
Nevertheless, we observed that for the acclimatized rice waste, H2 production decreased
after the 10th day with increase in biogas production. This was not the case for the non-
acclimatized, H2 and biogas production stabilized the same day.
The shorter lag period observed for acclimatized rice waste could be because
acclimatization hastened the activities of the hydrogen producing bacteria. The increasing
biogas in the acclimatized rice waste could be as a result of the presence of methanogenic
bacteria which were also enhanced by acclimatization even though they were affected by
pre-heating (Ueno, 2001; Ahn, 2005; Kim et al., 2006).
Statistical analysis nevertheless showed no significant difference (P = 0.05) when the
amount of hydrogen produced by acclimatized rice waste was compared with that of non-
acclimatized rice waste. However, Duncan multiple comparison test showed the amount of
biogas produced by acclimatized rice waste to be significantly higher when compared to
that of non-acclimatized rice waste (P = 0.0455).
86
Figure 4.9 Effects of Acclimatization on Cumulative Biogas and H2 Production Using Rice
Waste as Substrate
4.4.2 Effects of Acclimatization on Cumulative Biogas and H2 Production When Fish
Waste was Used as Substrate
Cumulative biogas production and H2 production commenced on day 3 for both
acclimatized and non-acclimatized fish waste substrate (Figure 4.10). A rapid increase in
biogas and H2 production was observed in the acclimatized fish waste as opposed to the
slow increase observed for the non-acclimatized substrate. The maximum H2 production
was 89.7 mL for acclimatized and 20 mL for the non-acclimatized fish waste substrate. We
also observed that H2 production stopped on the 8th day and on the 6th day for the
acclimatized and the non-acclimatized fish waste respectively. We observed that CO2
0
5
10
15
20
25
30
35
1 2 3 4 5 6 7 8 9 10 11 12Cu
mu
lati
ve
Bio
gas
an
d H
2P
rod
uct
ion
(m
L)
Days
Acclimatized Cumulative Biogas Production (mL)
Acclimatized Hydrogen
Non Acclimatized Cumulative Biogas Production (mL)
Non Acclimatized Hydrogen
87
production was increasing with a decrease in H2 content of the biogas both in both
experimental conditions.
Figure 4.10 Effect of Acclimatization on Cumulative Biogas and H2 Production when Fish
Waste was used as Substrate
The 3 day lag period in both conditions could be because acclimatization could not enhance
hydrogen production. Fish waste as observed in this study produced more carbon dioxide
than rice, vegetable and mixed waste substrate. Thus, reducing the effect of acclimatization.
This implies that in both conditions, H2 production commenced on the same day but the
difference is in the amount produced. It was also observed that the H2 production lasted
longer when acclimated fish waste was used as substrate than when non-acclimatized fish
0
20
40
60
80
100
120
140
160
180
200
1 2 3 4 5 6 7 8 9 10 11 12
Cu
mu
lati
ve
Bio
gas
an
d H
2P
rod
uct
ion
(m
L)
Fermentation Days
Acclimatized Biogas Cumulative Production(mL)
Acclimatized Hydrogen
Non Acclimatized Biogas Cumulative Production(mL)
Non Acclimatized Hydrogen
Non Acclimatized Cumulative Production
Acclimatized Cumulative Production
88
waste. This is probably because; acclimatized fish waste could withstand the carbon
dioxide effect longer than the non-acclimatized (Ren et al., 2006).
This result is in agreement with previous studies that acclimatization has effect on bio-
hydrogen production (Nasr et al., 2011; Voet et al., 1999). However, Dunn’s multiple
comparison test showed that the differences in cumulative biogas production was
statistically significant in the comparison between acclimatized fish waste and non-
acclimatized fish waste (P = 0.0006).
4.4.3 Effect of Acclimatization on Cumulative Biogas and H2 Production Using
Vegetable Waste as Substrate for Fermentation
Hydrogen production commenced on the 3rd day in the acclimatized vegetable waste and on
the 6th day for the non-acclimatized vegetable waste (Figure 4.11). It was observed that for
the acclimatized vegetable waste, H2 content increased with increasing biogas production. It
continued until a maximum of 45.24 mL on the 6th day was reached beyond which H2
production stabilized. When compared with non-acclimatized vegetable waste, H2 content
of biogas in the acclimatized vegetable was almost 80 % while that of the non-acclimatized
was less than 10 %. This shows that acclimatization enhanced H2 production by 70 %. It
might not be wrong to say that acclimatization reduced the formation of CO2 when
vegetable waste is used as substrate for bio-hydrogen production.
However, Dunn's Multiple Comparisons Test showed a higher significant difference (P =
0.0029) when the Cumulative biogas production of acclimatized vegetable waste was
compared with that of non-acclimatized. It further showed a higher significant difference (P
89
< 0.05) when the hydrogen produced by acclimatized vegetable waste was compared with
that of non-acclimatized vegetable waste.
The reason for the lower yield in non-acclimatized vegetable waste might be because the H2
production was sustained by acclimatization in the acclimatized vegetable. Accumulated
acidic medium will lower the pH of the reactor since the pH was not controlled. Thus, H2
producing bacteria involved were unable to sustain its metabolic activity (Nazlina et al.,
2009; Yap, 2013). It might as well be because only the indigenous microbe was in the
fermenter. Vegetables are also known to contain high amount of vitamins and minerals
(Leon, 2011) which can affect the pH of the medium, thus, affecting hydrogen production.
Figure 4.11 Effects of Acclimatization on Cumulative Biogas and H2 Production Using
Vegetable Waste as Substrate
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10 11 12
Cu
mu
lati
ve
Bio
gas
an
d H
2P
rod
uct
ion
(mL
)
Fermentation Days
Acclimatized Biogas Cumulative Production(mL)
Acclimatized Hydrogen
Non Acclimatized Biogas Cumulative Production(mL)
Non Acclimatized Hydrogen
Acclimatized Cumulative Biogas Production
Non Acclimatized Cumulative Biogas Production
90
4.4.4 Effect of Acclimatization on Cumulative Biogas and H2 Production Using
Mixed Food Waste as Substrate.
It was observed that Biogas production commenced on the 5th day in the acclimatized as
opposed to the non-acclimatized which commenced on the 6th day (Figure 4.12). A rapid
increase in H2 production was observed in the acclimatized non-acclimatized experimental
conditions from the 6th and 7th day respectively. Furthermore we observed that biogas and
H2 gas production seems to stabilize on the 9th day for acclimatized and on the 10th day for
the non-acclimatized mixed food waste. The maximum H2 production was 130.95 mL for
acclimatized and 33.3 mL for non-acclimatized mixed food waste substrate.
Figure 4.12 Effects of Acclimatization on Cumulative Biogas and H2 Production Using
Mixed Food Waste as Substrate
0
20
40
60
80
100
120
140
160
1 2 3 4 5 6 7 8 9 10 11 12Cu
mu
lati
ve
Bio
gas
an
d H
2p
rod
uct
ion
(m
L)
Fermentation Days
Acclimatized Cumulative Biogas Production
Acclimatized Hydrogen
Non Acclimatized Cumulative Biogas Production
Non Acclimatized Hydrogen
91
The long lag period observed in both acclimatized and non-acclimatized food waste
substrate could be because of the heterogeneous nature of the substrate. Being mixed, it has
various components which also have various rates of decomposition. The 97.65 mL
difference in the maximum H2 yield could be because the hydrogen producing bacteria in
the non-acclimatized were not much and so cannot sustain the gas production (Nasr et al.,
2011).
Statistical analysis showed that H2 produced by acclimatized vegetable was significantly
more than that produced by the non-acclimatized vegetable waste (P < 0.0001).
From this study, it is obvious that acclimatization improved the H2 yield from the different
food waste substrates used for bio-H2 production. This study agrees with previous studies
(Fang et al 2006, Massanet et al 2008, Nazlina et al. 2011) where acclimatization was used
to enhance bio-H2. Nevertheless, some studies also showed enhanced bio-hydrogen
production without acclimatization (Kim et al., 2004 and Pan et al., 2008).
4.5 Gompertz Kinetic Model
This is a kinetic model used to determine the hydrogen production potential (P) and
hydrogen production rate (Rm) of the different food waste used as substrates.
Mixed food waste was observed to have higher rate of H2 production than other food waste
substrates followed by rice, fish and lastly vegetable (Table 4.5). Vegetable waste had the
lowest H2 production rate while mixed food waste has the highest H2 production rate. It is
interesting to note that rice recorded the highest H2 production potential, followed by mixed
92
food waste, fish and vegetable. It was also observed that the cumulative H2 production of
mixed food waste substrate is higher 130.95 mL while fish, rice and vegetable were 26.97
mL, 30 mL, and 31 mL respectively.
Table 4.5 H2 Production rate and Production Potential for Acclimatized Food Waste
Substrate
FWS Rm (mL/d) ƛ H (mL) ƛ-t Rm.e P (mL)
Rice 41.215 1 26.97 -10 112.02 83.04
Fish 30.7 2 30 -9 83.44 55.8
Vegetable 16.1 1 31.72 -10 43.76 32.7
Mixed 60.5 5 130.95 -6 164.44 74.2
FWS = food waste substrate, Rm = maximum hydrogen production rate (mL/d), H =
cumulative hydrogen production (mL), T = time (11 days), ƛ = lag period, P = hydrogen
production potential (mL), e = exponential (2.718)
The higher H2 production rate by mixed food waste might be because mixed waste has
higher organic load. Higher organic loads has been reported to increase hydrogen
production yield (Chen et al., 2006; Kraemer, 2007). It could also be because mixed food
waste also contains some rice and other carbohydrate food sources which could enhance
bio-hydrogen production.
The highest H2 production potential by rice waste is probably because of rice is a rich
source of carbohydrate while fish is a rich source of protein, vegetable, a rich source of
vitamins and minerals (Leon, 2011; Steele, 2011; Yap, 2013). Mixed food waste having
93
more iron tends to have lower H2 production potential (Liu and Shen 2004). Higher
cumulative H2 by mixed food waste substrate can be attributed to the fact that much (60 % -
90 %) of the biogas it produced was H2 (Guo et al., 2010; Keigo and Shigeharu, 2006).
From this Gompertz kinetic model, it can be concluded that even though rice has the
highest H2 production potential, mixed food waste produced H2 faster than rice.
Table 4.6 shows the Gompertz kinetic parameters for non-acclimatized food waste
substrates. Fish waste and mixed waste seems to have the same H2 production potential
with mixed waste having the high H2 production rate which suggest that acclimatization
was a great boost for the microbes in the mixed waste but not that great in the fish waste. It
was also observed that even though vegetable waste and mixed waste had the same lag
period of 4 days, the H2 production potential of mixed waste is 15.5 mL more than that of
vegetable. This might be because, the mixed waste is a combination of rice waste, fish
waste and vegetable waste substrates. It is also evident that even though gas production
started after 2 days for rice waste and fish waste, rice waste produced H2 faster and also has
a higher H2 production potential then the fish waste. This might also be attributed to rice
being a rich source of carbohydrate. It could also be as because 80 % - 90 % of the biogas
content measured from rice waste was hydrogen (Pan et al., 2013)
This study agrees with previous studies with mixed food waste having a relatively high H2
production rates (Jayalakshmi et al., 2007, Karlsson et al., 2008). The difference in H2 yield
in comparison with the current study could be attributed to the difference in reactor types
used. A previous study by Dong et al. (2009) revealed that rice has a greater H2 production
94
potential than the other food waste substrates studied in this research. This is in agreement
with the current study.
Gompertz kinetic model was also used to determine if acclimatized food waste has higher
H2 production potential than the non-acclimatized food waste. It was shown that the
difference in the rate of H2 production was 19.7 mL/d, 20.95 mL/d, 15.55 mL/d and 49
mL/d for rice waste, fish waste, vegetable waste and mixed food waste. This means that
when compared to the non-acclimatized substrates, the rate at which H2 is produced in the
four acclimatized substrates was twice the rate at which H2 was produced in non-
acclimatized condition. Furthermore, we also observed that the hydrogen production
potential of the acclimatized food waste substrates were greater than those of the non-
acclimatized food waste substrates by 44.04 mL for rice waste, 38.1 mL for fish waste, 31.9
mL, 57.9 mL. These values were more than twice that of non-acclimatized food waste
substrates. It will be necessary to analyze the individual differences within each condition.
Table 4.6 H2 Production rate and production potential for non-acclimatized Food
waste Substrate
FWS Rm (mL/d ƛ H (mL) ƛ-t Rm.e P (mL)
Rice 21.5 2 13.6 -9 58.44 39
Fish 9.75 2 13.6 -9 26.5 17.7
Vegetable 0.55 4 1.04 -7 1.49 0.8
Mixed 11.5 4 10 -7 31.257 16.3
FWS = food waste substrate, Rm = maximum hydrogen production rate (mL/d), H =
cumulative hydrogen production (mL), T = time (11 days), ƛ = lag period, P = hydrogen
production potential (mL), e = exponential (2.718)
95
Acclimatization of food waste with anaerobic sewage sludge will not only remove food
waste from the MSW that goes to landfill, it will also remove the sludge from water and
waste water treatment plants. The product after the experiment can also be used as compost.
Therefore, it will not only be a useful resource for H2 production, but can also be
composted to provide nutrient supplement for plants (Okamoto, 2000).
4.6 Effect of Metal Ions Concentration on Bio-Hydrogen Production
One common metallic ion which can be found in MSW stream is lead (Pb). This is
contained in batteries which were not separated before disposal. Thus a study to see if food
waste containing this metallic ion can be used as a substrate for bio-H2 production was
conducted. The effect of different concentration of Pb in bio-H2 production from food waste
substrate is discussed in this section.
4.6.1 Effect of Metal ion Concentration of 5 mg/l of Pb on Bio-Hydrogen
Production
Figure 4.13 shows the effect of 5 mg/L of Pb concentration on the bio-hydrogen production
from food waste. It was observed that biogas and H2 production commenced after day one.
The reaction time for the control experiment was just 2 days after a lag period of 1 day as
opposed to 6 days reaction time observed in the food waste with 5 mg/l of Pb. The biogas
and hydrogen production increased until a maximum of 16.6 mL of H2 was produced on the
5th day as opposed to 10.3 mL of H2 on the 3rd day for the control. Beyond the 5th day, H2
content of the biogas dropped to 3.7 mL for the food waste with 5 mg/L of Pb while no gas
production was observed after the 3rd day for the control.
96
Figure 4.13 Effect of metallic ion (5 mg/L of Pb) on Bio-Hydrogen Production from Food
Waste. CGB => cumulative Biogas Production
The difference observed in reaction days could be because lead ion at this trace
concentration was a co-factor to the transport of hydrogenase thus making the reaction days
longer (Wang and Wan, 2009). The decrease observed after day 5 could be when the lead
ion became toxic to the system. It is important to note that no methane was observed
throughout the experiment. We could say that the presence of lead at 5 mg/L was also an
inhibitor to methane forming bacteria (Wang and Wan, 2009).
4.6.2 Effect of Metal ion Concentration at 10 mg/L on Bio-H2 Production
It can be observed from Fig 4.14, that gas production started after the 1st day, nevertheless,
the biogas and H2 produced by the mixture containing 10 mg/L of lead was lower than the
control. After the 3rd day, gas production in the control reduced to zero while that in food
wastes containing 10 mg/L of Pb was on the increase. The maximum H2 yield of 41.6 mL
-5
0
5
10
15
20
25
30
35
1 2 3 4 5 6Cu
mm
ula
tive
Bio
gas
an
d H
yd
rogen
Pro
du
ctio
n (
mL
)
Fermentation Days
Average CBG Average H2
Control Average CBG Control average H2H2
H2
97
was recorded on the 5th day for the food waste with 10 mg/L of Pb while that of the control
was 10.3 mg/L on the 3rd day. There was a drop in H2 production on the 6th day to 1.8 mL.
It was observed that the maximum H2 from food waste with 10 mg/L was considerably
more than that from 5 mg/L.
Figure 4.14 Effect of metallic ion (10 mg/L of Pb) on bio-hydrogen production from food waste.
The lower H2 yield by the food waste with 10 mg/L could be due to the time it took for the
Pb to be evenly distributed into the cells of the indigenous bacteria (Stohs and Bagchi,
1995). This result is in agreement with previous studies that increase in the concentration
of metal ions increases the hydrogen yield (Sinha and Pandey, 2011; Wang and Wan,
-10
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6Cu
mm
ula
tive
Bio
gas
an
d H
2p
rod
uct
ion
(m
L)
Fermentation Days
Average CBG Average H2
Control Average CBG Control average H2H2
H2
98
2009). However, the H2 yield varies in these studies which could be due to the substrates
and types of reactors used.
4.6.3 Effect of Metal ion Concentration at 15 mg/L on Bio-Hydrogen
Production
From Fig 4.15, it was observed that biogas and H2 production increased simultaneously
after a 1 day lag period until after the 5th day when the H2 content of the biogas dropped to
almost zero. Maximum H2 production of 52.6 mL was recorded on the 5th day which was
higher than 10.3 mL recorded as maximum H2 production for the control. With a difference
of 42.3 mL, one can say that addition of 15 mg/L of lead increased the production of H2.
The low yield observed through the experiment after the 5th day could be because the
readily useable carbohydrate had been used up by the H2 producing bacteria which in turn
led to the stop in H2 (Fadhil and Maleek, 2010). The high yield experienced throughout the
3 levels used in this study could be because the presence of metal ion in fermentation
medium facilitate the bacterial growth by increasing the percentage of glucose consumed
thereby increasing the H2 productivity (Fadhil and Maleek, 2010).
Despite the changes in H2 production observed at different level of Pb addition, the H2
produced at these levels showed no statistical significance (P = 0.2) but it was only
significant when compared with the control (P = 0.001).
99
Figure 4.15 Effect of metal ion (15 mg/L of Pb) on Bio-Hydrogen production from food
waste
It has been reported that metal ion in trace levels enhance H2 production and this is
supported by this result, for example, the photosynthetic bacteria, Rodospirillumrubrum,
produced H2 when grown in cheese whey in presence of light, then the addition of Fe ions
(5 mg/L) enhanced H2 production of treated whey to about 6000 ml in 10 days (Fadhil and
Maleek, 2010). In another study, trace metal addition showed enhanced H2 yield from 391
mLg−1 to 408 mLg−1 (Hisham et al., 2008). It has also been observed that metals such as
Magnesium and calcium additions were better for growth of bacteria and not for H2
production (Fadhil and Maleek, 2010).
-10
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6Cu
mm
ula
tive
Bio
gas
an
d h
yd
rogen
Pro
du
ctio
n
(mL
)
Days
Average CBG Average H2
Control Average CBG Control average H2
100
4.7 Gompertz Kinetic Parameters for Metallic ion content
The control and the medium with metal additions had the same lag period of 1 day while
the highest cumulative H2 production was at 15 mg/L (Table 4.7). One could then say that
the cumulative H2 production increased as the concentration of the metal ions increases,
with 5 mg/L for 44 mL/d, 10 mg/L for 102 mL/d and 15 mg/L for approximately 120 mL/d.
It was also observed that the mixture with the metal ions have higher H2 production rates
and higher H2 production potential than the control. All these parameters were also
increasing with increase in metal ion concentration.
Table 4.7 H2 Production Rate and Potential
FWS = food waste substrate, Rm = maximum hydrogen production rate (mL/d), H =
cumulative hydrogen production (mL), T = time (11 days), ƛ = lag period, P = hydrogen
production potential (mL), e = exponential (2.718).
Considering the H2 production potential, 5 mg/L was 3.3 mL greater than the control, 10
mg/L was 11.11 mL greater than the control and 15 mg/L was 12.25 mL greater than the
Conc. Rm
(mL/d)
ƛ H(mL) ƛ-t Rm.e P (mL)
Control 5.15 1 5.15
-2 14.0 2.12
5mg/L 6.2 1 44 -4 16.85 5.42
10mg/L 15.2 1 102.3 -4 41.31 13.23
15mg/L 16.4 1 119.9 -4 44.58 14.37
101
control. Considering the H2 production rates, 5 mg/L was 0.05 mL/d greater than the
control while 10 mg/L and 15 mg/L were 10.05 mL/d and 11.25 mL respectively greater
than the control. The result got from Gompertz kinetic model revealed that food waste with
trace amounts of lead ion has the potential to produce H2 even more than the food waste
without lead (Nasr et al., 2011).
Both the control and food waste with metal ions having the same lag period could be
because lead ions had not been absorbed properly and as such could not catalyze the
reaction faster than it had started (Wang and Wan, 2009). The increase in hydrogen yield as
the concentration lead ion increased may be because lead ion served as a nutrient
supplement for hydrogenase, thus increasing hydrogen production (Heidrich and
Witkowski, 2010).
The problem with this method would be where to dispose this waste after it has been used
for H2 production. This is because it now contains metallic ions which have the ability to
bio-accumulate and cause various problems in any environment. For example, Lead can
cause: disruption of the biosynthesis of haemoglobin and anaemia, rise in blood pressure,
kidney damage, miscarriages and subtle abortions (Lenntech, 2013).
4.8 Column Experiments
This section used batch reactor to know its effect on bio-hydrogen production. However,
this experiment was conducted using mixed food waste substrate.
Figure 4.16, 4.17 and 4.18 shows the effect of metal ion concentration of 5 mg/L, 10 mg/L
and 15 mg/l on bio-hydrogen production in a column respectively. The biogas contained in
the column only consists of H2 and CO2.
102
4.8.1 Effect of 5 mg/L of Pb on Bio-hydrogen Production using Food Waste as a
Substrate
Biogas production commenced on the second day for both the control and the food waste
with Pb ion at 5 mg/L (Fig 4.16). The control was observed to produce its maximum biogas
of 48 mL on the second day. However, the maximum hydrogen yield by the control was
10.3 mL on the 3rd day. The food waste with 5 mg/L of Pb produced a maximum biogas of
68 mL on the 6th day. Furthermore, it showed a maximum hydrogen yield of 42.96 mL on
the 4th day beyond which hydrogen production was stabilized.
Figure 4.16 Effect of Metal ions (5 mg/L of Pb) on bio-hydrogen production. CBG
Cumulative Biogas
The difference observed in the lag period could be because concentration of the ion did not
affect the lag period. This agrees with a previous study Liu et al, 2009. The higher amount
of biogas and hydrogen observed in the food waste with 5 mg/L of lead could be due to the
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6
Cu
mu
lati
ve
Bio
gas
an
d H
yd
rogen
pro
du
ctio
n
(mL
)
Fermentation Days
CBG Hydrogen Control CBG Control Hydrogen
103
lead it contains. This was possible because a trace level of the ions is required for activation
of function of many enzymes including the hydrogenase (Zheng et al., 2005). The
inhibition after 6 days could be mostly due to the disruption of the hydrogenase structure
because of its chemical bonding to Pb (Zheng et al., 2005).
4.8.2 Effect of 10 mg/L of Pb on Bio-hydrogen Production using Food Waste as a
Substrate
Biogas production commenced on the second day for both the control and the food waste
with Pb ion at 10 mg/L (Fig 4.17). A decreasing order in biogas and hydrogen production
was observed in the control while the reverse was the case in the food waste with 10 mg/L
of Pb. The control produced maximum biogas of 48 mL on the second day as opposed to
maximum biogas production 185 mL by food waste with 10 mg/L.
However, the control has a maximum hydrogen yield of 10.3 mL while food waste with 10
mg/L has 124.8 mL. Gas production stopped after the 3rd day in the control while it stopped
after the 6th day in the food waste with 10 mg/L of Pb. It is important to note that at the
control had 40 % of its biogas as hydrogen at the last day while the food waste with 10
mg/L of Pb had less than 10 % of its biogas content as hydrogen.
The higher biogas and hydrogen produced by the food waste with 10 mg/L of lead could be
because lead acts as a co-enzyme factor hydrogenase, thus increases increasing its
transportation and action across the system (Heidrich and Witkowski, 2010). It could as
well be the reason why the fermentation days were longer than the controls’.
104
Figure 4.17 Effect of Metal ions (10 mg/L of Pb) on Bio-hydrogen production using food
waste as substrate.
CBG Cumulative Biogas
4.8.3 Effect of 15 mg/L of Pb on Bio-hydrogen Production using Food Waste as a
Substrate
The control and the food waste with Pb ion at 10 mg/L commenced biogas production on
the second day (Fig 4.18). A decreasing order in biogas (48 mL, 26 mL and 17 mL) was
observed in the control while the reverse (28.5 mL, 69 mL, 118.5 mL, 193.5 mL and 201
mL) was the case in the food waste with 15 mg/L of Pb. Maximum hydrogen yield of
157.95 mL was observed for food waste containing Pb ions as opposed to 10.3 mL
observed in the control.Just like the previous lead ion concentrations of 5 mg/L and 10
mg/L, the fermentation period was also 6 days for 15 mg/l and 4 days for the control. On
0
50
100
150
200
250
1 2 3 4 5 6
Cu
mm
ula
tive
Bio
gas
an
d H
yd
rogen
Pro
du
ctio
n
(mL
)
Days
CBG Hydrogen Control CBG Control Hydrogen
105
the 6th day, only 5 % of the biogas produced by food waste with 15 mg/L was hydrogen
while the rest 95 % was CO2. This could be because at this stage Pb has effectively bonded
with hydrogenase thus reducing its potency to produce hydrogen (Stohs and Bagchi, 1995).
It could be said be said that the more the fermentation days, the less the hydrogen produced
and the more the CO2 produced. This will in turn acidify the system, which lowers the pH,
thus reducing hydrogen production until no hydrogen will be produced (Yu et al., 2010).
Figure 4.18 Effect of Metal ions (15 mg/L of Pb) on Bio-hydrogen production using food
waste as substrate.CBG Cumulative Biogas
This study is in agreement with previous studies showing that trace amount of metal ions
improve hydrogen production but also inhibits hydrogen production on a longer
fermentation days (Hakobyan et al., 2012; Heidrich and Witkowski, 2010; Hisham et al.,
2008; Sinha and Pandey, 2011; Wang and Wan, 2009).
0
50
100
150
200
250
1 2 3 4 5 6
Cu
mm
ula
tive
Bio
gas
an
d H
yd
rogen
prd
uct
ion
(mL
)
Fermentation Days
CBG Hydrogen Control CBG Control Hydrogen
106
In comparison with the hydrogen produced when Pb ions were added to the bottle
experiment, the column hydrogen yield tends to be 3 times more. This could be because of
the higher amount of substrate used for the column study. However, there was no
significant difference when hydrogen produced from bottle experiment with Pb ions was
compared to that produced from column experiment.
107
CHAPTER 5
CONCLUSION
In this current study, hydrogen was produced from different food waste substrates with rice
having the highest hydrogen production potential. However a combination of the food
waste was also a good substrate for bio-hydrogen production. Temperature of 350C and pH
5.5 were found to be optimal when considering the optimum parameters for bio-hydrogen
production. Acclimatization with anaerobic sewage sludge was found to enhance bio-
hydrogen production through dark fermentation process. Hydrogen production potential
and hydrogen production rate of the food waste substrates were determined using the
Gompertz kinetic model in which rice waste and mixed waste showed highest hydrogen
production potential and the highest hydrogen production rate respectively. Addition of
metal ion such as Pb ions in trace levels also enhanced bio-hydrogen production.
108
REFERENCES
Abdul Rahman D. (2013). Solid Waste Management in Malaysia. International Conference
On Waste Management and Environment, University of Malaya, Malaysia, Borneo Post
online. doi: http://dx.doi.org/10.1016/j.enpol.2005.04.003
Agamuthu P. (2001). Solid Waste: Principles and Management. Malaysia, University of
Malaya Press.
Agamuthu P. (2009). Challenges and opportunities in agro-waste management: An Asian
perspective. Paper presented at the Inaugural meeting of first regional 3R forum in Asia.
Agamuthu P. (2014). MSW Management in Malaysia-Changes for Sustainability.
Municipal Solid Waste Management in Asia and the Pacific Islands. Agamuthu, P and
Tanaka, M. Springer Singapore: 195-232.
Ahn Y. P. E., Oh YK, Park S., Webster G., Weightman A.J. (2005). Biofilm microbial
community of a thermophilic trickling biofilter used for continuous biohydrogen
production. FEMS Microbiol Lett. 249(1), 31-38.
Akutsu Y., Li Y.Y., Harada H., and Yuc H.Q. (2009). Effects of temperature and substrate
concentration on biological hydrogen production from starch. International Journal of
Hydrogen Energy 34(6): 2558-2566.
Allakhverdiev S. I. (2012). Photosynthetic and biomimetic hydrogen production.
Interernational Journal of Hydrogen Energy 37(10): 8744-8752.
109
APHA A. (2005). Standard Methods for the Examination of Water and Wastewater. 21st
ed. American Public Health Association. Washington, DC. Part, 8000, 94-100.
Armaroli N, and Balzani, V. (2011). The hydrogen issue. Chem Sus Chem 4(1): 21-36.
Arvizu D, Palani B., Luisa F. C., Terry H. K. G., Arnulf J.-W., Michio K., Charles K., et al.
(2011). Technical Summary. IPCC Special Report on Renewable Energy Sources and
Climate Change Mitigation. O. Edenhofer, R. Pichs-Madruga, Y. Sokonaet al. Cambridge,
United Kingdom and New York, NY, USA, Cambridge University Press.
Atif A. A. Y., Fakhru’l-Razi A., Ngan M. A., Morimoto M., Iyuke S. E., and Veziroglu N.
T. (2005). Fed batch production of hydrogen from palm oil mill effluent using anaerobic
microflora. International Journal of Hydrogen Energy 30(13–14): 1393-1397. doi:
http://dx.doi.org/10.1016/j.ijhydene.2004.10.002
Avasthi K. S., Reddy R. N. and Patel S. (2013). Challenges in the Production of Hydrogen
from Glycerol – A Biodiesel Byproduct Via Steam Reforming Process. Procedia
Engineering 51(0), 423-429. doi: http://dx.doi.org/10.1016/j.proeng.2013.01.059
Balmer M. and Spreng D. (2008). Chapter 11 - Hydroelectric Power. In M. L. Trevor (Ed.),
Future Energy. Oxford: Elsevier. Pp. 193-209.
Baron, S. (1996). Medical microbiology. Galveston. Texas, University of Texas Medical
Branch
110
Bao M. D., Su H. J., and Tan T. W. (2013). Dark fermentative bio-hydrogen production:
Effects of substrate pre-treatment and addition of metal ions or L-cysteine. Fuel 112(0): 38-
44. doi: http://dx.doi.org/10.1016/j.fuel.2013.04.063
Basu S., Asim L K., Angels C.-O., Chunqing L., and Ivo FJ V. (2010). Membrane-based
technologies for biogas separations. Chemical Society Reviews 39(2): 750-768.
Baxter L. (2005). Biomass-coal co-combustion: opportunity for affordable renewable
energy. Fuel, 84(10), 1295-1302.
BP (2010) Statistical Review of World Energy
Capareda S. P. (2011). Biomass Energy Conversion, Sustainable Growth and Applications
in Renewable Energy Sources, Dr. Majid Nayeripour (Ed.), ISBN: 978-953-307-408-5,
InTech, Available from: http://www.intechopen.com/books/sustainable-growth-and-
applications-in-renewable-energy-sources/biomassenergy-conversion.
Carlos Ramos G., Iva´n Moreno-Andrade B., Chamy R. (2012). Effect of the initial total
solids concentration and initial pH on the bio-hydrogen production from cafeteria food
waste. International Journal of Hydrogen Energy: 1 - 8.
Chen W.-H., Chen S.-Y., Kumar Khanal S., and Sung S. (2006). Kinetic study of biological
hydrogen production by anaerobic fermentation. International Journal of Hydrogen Energy
31(15): 2170-2178. doi: http://dx.doi.org/10.1016/j.ijhydene.2006.02.020
111
Chen Y., Naidong X., Yuxiao Z., and Hui M. (2012). Enhancement of hydrogen production
during waste activated sludge anaerobic fermentation by carbohydrate substrate addition
and pH control. Bioresource Technology 114(0): 349-356.
Chinellato G., Cavinato C., Bolzonella D., Heaven S. and Banks C. J. (2013). Biohydrogen
production from food waste in batch and semi-continuous conditions: Evaluation of a two-
phase approach with digestate recirculation for pH control. International Journal of
Hydrogen Energy 38(11): 4351-4360.
Chu C.-F., Li Y.-Y., Xu K.-Q., Ebie Y., Inamori Y., and Kong H.-N. (2008). A pH- and
temperature-phased two-stage process for hydrogen and methane production from food
waste. International Journal of Hydrogen Energy 33(18): 4739-4746. doi:
http://dx.doi.org/10.1016/j.ijhydene.2008.06.060
Chum H., Faaij A., Moreira J., Berndes G., Dhamija P., Dong H., Pingoud K. (2011).
Bioenergy. In O. Edenhofer, R. Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S.
Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer and C. von Stechow (Eds.),
IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation.
Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
Chyi-How L., Chin-Chao C., How-Chih L., Chian-Yu L., Chia-Wen L., and Chiu-Yue L.
(2010). Optimal Ph And Substrate Concentration For Fermentative Hydrogen Production
From Preserved Fruits Soaking Solution J. Environ. Eng. Management 20(1): 35-41.
112
Cicia G., Cembalo L., Del Giudice T., and Palladino A. (2012). Fossil energy versus
nuclear, wind, solar and agricultural biomass: Insights from an Italian national survey.
Energy Policy 42: 59-66.
Consonni S. and Viganò F. (2012). Waste gasification vs. conventional Waste-To-Energy:
A comparative evaluation of two commercial technologies. Waste Management 32(4): 653-
666.
Daniel H. and Natalie G. (2005). Managing municipal solid waste in Latin America and the
Caribbean Public Private Infrastructure Advisory Facility. Washington, DC 20433, USA,
Dann C., Vandenberg J. et al. (2012). Reconsidering Waste-to-Energy. Public Utilities
Fortnightly 150(3): 44-51.
Das K. M. and Debabrata (2012). State of the Art and Progress in Production of
Biohydrogen. A. Nuri, David, B, Levin. India, Bentham Science Publishers: 127-136.
Doman L . (2006). International Energy Outlook 2006. Energy Information Administration
No. DOE/EIA-0484.
Dong L., Zhenhong Y., Yongming S., Xiaoying K., and Yu Z. (2009). Hydrogen
production characteristics of the organic fraction of municipal solid wastes by anaerobic
mixed culture fermentation. International Journal of Hydrogen Energy 34(2): 812-820. doi:
http://dx.doi.org/10.1016/j.ijhydene.2008.11.031
Dorian J. P., Franssen H. T. and Simbeck D. R. (2006). Global challenges in energy.
Energy Policy 34(15): 1984-1991.
113
EERE (2011). U.S. Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts
Industry. U. S. D. o. Energy. Oak Ridge National Laboratory, Oak Ridge: 227.
Elijah T. I., Ibifuro A. M. and Yahaya S. M. (2009). The study of cow dung as co-substrate
with rice husk in biogas production. Scientific Research and Essay 4: 861-866.
Energy Information Administration (EIA 2011). U. S. Annual Energy Outlook with
projection to 2035.
EPA (2012). A life cycle assessment of emission and sinks. Solid Waste management and
Green house gases. Washinton DC, U.S. Environmental Protection Agency.
Eroğlu E., İnci E., Ufuk G., Lemi T., and Meral Y. (2006). Biological hydrogen production
from olive mill wastewater with two-stage processes. International Journal of Hydrogen
Energy 31(11): 1527-1535.
Fang H. H. P., Li C. and Zhang T. (2006). Acidophilic biohydrogen production from rice
slurry. International Journal of Hydrogen Energy 31(6): 683-692. doi:
http://dx.doi.org/10.1016/j.ijhydene.2005.07.005
Fadhil M. S. and Maleek M. I. (2010). Influence of Metal Ions on Hydrogen Production by
Photosynthetic Bacteria Grown in Escherichia coli Pre-Fermented Cheese Whey. Journal
of Environmental Protection 1: 426-430.
Fauziah S. H. and Agamuthu P. (2008). Challenges and issues in moving towards
sustainable landfilling in a transitory country - Malaysia. Waste Manag Res., 29(1): 13-19.
114
Fernández-Morales F. J., Villaseñor J. and Infantes D. (2010). "Modeling and monitoring
of the acclimatization of conventional activated sludge to a biohydrogen producing culture
by biokinetic control." international journal of hydrogen energy 35(20): 10927-10933.
Gerardi M. H. (2003). The microbiology of anaerobic digesters. John Wiley and Sons.
Güllü D. and Demirbaş A. (2001). Biomass to methanol via pyrolysis process. Energy
Conversion and Management 42(11): 1349-1356. doi: http://dx.doi.org/10.1016/S0196-
8904(00)00126-6
Guo X. M., Trably E., et al. (2010). Hydrogen production from agricultural waste by dark
fermentation: A review. International Journal of Hydrogen Energy 35(19): 10660-10673.
Hakobyan L., Gabrielyan L., Armen T. (2012). Ni (II) and Mg (II) ions as factors
enhancing biohydrogen production by Rhodobacter sphaeroides from mineral springs.
International Journal of Hydrogen Energy 37(9): 7482-7486.
Hallenbeck P., C. (2009). "Fermentative hydrogen production: Principles, progress, and
prognosis." International Journal of Hydrogen Energy 34(17): 7379-7389.
Han S.-K. and Shin H.-S. (2004). Biohydrogen production by anaerobic fermentation of
food waste. International Journal Of Hydrogen Energy 29(6): 569-577.
Hanaoka T., Fujimoto S., Yoshida T., Kamei K., Harada M., Suzuki Y., . . . Minowa T.
(2004). Hydrogen production from woody biomass by novel gasification using CO2
115
Sorbent. In J.-S. C., Sang-Eon P. and L. Kyu-Wan (Eds.), Studies in Surface Science and
Catalysis 153: 103-108.
Hariklia N., Gavala I. V.,Birgitte S., and Ahring K. (2006). Biological hydrogen production
in suspended and attached growth anaerobic reactor systems. International Journal Of
Hydrogen Energy 31: 1164 – 1175.
Harun K, İnci E, Ufuk G, Meral Y, Lemi T. (2003). Kinetics of biological hydrogen
production by the photosynthetic bacterium Rhodobacter sphaeroides O.U. 001 : Koku, H.
et al. International Journal of Hydrogen Energy 28(4): 381–388.
Heidrich Z. (2004). Sewage system. Wydawnictwo WSiP.
Heidrich Z. and Witkowski A. (2010). Equipment for sewage treatment. Design examples
of calculations. Wydanie II, Wydawnictwo „Seidel – Przywecki, Sp. z o.o.
Herbert P.F. and Hong L. (2002). Effect of pH on Hydrogen Production from glucose by
mixed culture. Bioresource Technology 82: 87-93.
Hisham A, Mohd S. K, Aidil A. H, and Wan M, Wan Y. (2008). Trace Metal Effect on
Hydrogen Production Using C.acetobutylicum. Online Journal of Biological Sciences 1(8):
1-9.
Hoornweg D. and Perinaz T. B (2012). What a waste : a global review of solid waste
management. Urban development series. U. D. S. k. papers. Washinton DC. 15.
116
Hori M., Matsui K., Tashimo M., and Yasuda I. (2005). Synergistic hydrogen production
by nuclear-heated steam reforming of fossil fuels. Progress in Nuclear Energy, 47(1–4),
519-526. doi: http://dx.doi.org/10.1016/j.pnucene.2005.05.053
Hou Y., Wang S., Zhou Y., Yan F., and Zhu J. (2013). Analysis of the carbon dioxide
concentration in the lowest atmospheric layers and the factors affecting China based on
satellite observations. International Journal of Remote Sensing, 34(6), 1981-1994.
Hurley E. E. (2009). Securing Australia's Energy for the Future: Kokoda Foundation.
Hyways (2007). The European hydrogen roadmap. www.Hyways.de.
IPCC, Ed. (2007). Climate Change 2007: Mitigation. Contribution of working Group III to
the fourth assessment Report of the Intergovernmental panel on climate Change. Waste
Management, Cambridge University Press.
IPCC (2011). IPCC Special Report on Renewable Energy Sources and Climate Change
Mitigation. Summary for Policymakers. Y. S. R.P.-M. O. Edenhofer, K. Seyboth, P.
Matschoss, S. Kadner, T. and P. E. Zwickel, G. Hansen, S. Schlömer, C. von Stechow.
Cambridge, United Kingdom and New York, NY, USA, Cambridge University.
Jagadish H P, Ma L, Raj A, Gavima C. C., and Thonart P. (2011). Study on Effect Of
Pretreatment Methods on Biomethanation Of Water Hyacinth. International Journal of
Advanced Biotechnology and Research 2(1): 143-147
117
Jaworski, C. (2007). UF Helps Animals Get Leftover Treats From Theme Parks and
Restaurants. Retrieved 19th June, 2013, from http://news.ufl.edu/1997/11/25/food.
Jayalakshmi S., Sukumarak K., and Kurian J. (2007). Hydrogen production from kitchen
waste using heat treated anaerobic biogas plant slurry. International Sustainable Solid
Waste Management. 34(21), 8854-8858. doi:
http://dx.doi.org/10.1016/j.ijhydene.2009.08.048
Jean-Pierre P. (2010). Membrane reactors for power stations. Dutch newsletter.
Netherlands.
Jianlong W. and Wan W. (2009). Factors Influencing Fermentative Hydrogen Production:
A Review. International Journal of Hydrogen Energy 34: 799–811
Jingwei Ma, Shuizhou K., Yinguang C. (2008). Mesophilic Biohydrogen Production from
Food Waste. Bioinformatics and Biomedical Engineering, 2008. ICBBE 2008.
Johari A., Saeed I. A., Haslenda H., Habib A., and Mat R. (2012). Economic and
environmental benefits of landfill gas from municipal solid waste in Malaysia. Renewable
and Sustainable Energy Reviews 16(5): 2907-2912.
Jong k., Kim., Le Nhat., Young N, Chun, S, Wouk, K. (2008). Hydrogen Production
Conditions from Food Waste by Dark Fermentation with Clostridium beijerinckii KCTC
1785. Biotechnology and Bioprocess Engineering 13: 499-504.
118
Kalinci Y., Arif H., and Ibrahim D. (2009). Biomass-based hydrogen production: A review
and analysis. International Journal Of Hydrogen Energy 34(21): 8799-8817.
Kalogo Y. and Bagley D. M. (2008). Fermentative hydrogen gas production using biosolids
pellets as the inoculum source. Bioresource Technology 99(3): 540-546.
Karak T., Bhagat R., and Bhattacharyya P. (2012). Municipal solid waste generation,
composition, and management: the world scenario. Critical Reviews in Environmental
Science and Technology 42(15): 1509-1630.
Karlsson A., Vallin L., and Ejlertsson J. (2008). Effects of temperature, hydraulic retention
time and hydrogen extraction rate on hydrogen production from the fermentation of food
industry residues and manure. International Journal of Hydrogen Energy 33(3): 953-962.
doi: http://dx.doi.org/10.1016/j.ijhydene.2007.10.055
Keigo Y. and Shigeharu T. (2006). Fermentative Hydrogen Production from Artificial Food
Wastes. WHEC 16. Lyon France.
Kijo-Klecckzkowska A., Otwinowski H. and Sroda K. (2012). Properties and production of
sewage sludge in Poland with reference to the methods of neutralizing. Archives of Waste
Management and Environmental Protection 14(4): 59-78.
Kim, Sang-Hyoun H, Sun-Kee S, Hang-Sik. (2004). Feasibility of Biohydrogen Production
by Anaerobic Co-Digestion of Food Waste and Sewage Sludge. International Journal of
Hydrogen Energy 29(15): 1607-16.
119
Kim S.H., Han S.K. and Shin H.S. (2006). Effect of substrate concentration on hydrogen
production and 16S rDNA-based analysis of the microbial community in a continuous
fermenter. Process Biochemistry 41: 199-207.
Kim D. H., Kim S.-H., and Shin H. S. (2009). Hydrogen Fermentation of Food Waste
Without Inoculum addition. Enzyme and Microbial Technology 45: 181-187.
Kim D.-H., Jieying W., Kyung-Won J., Mi-Sun K., and Hang-Sik S. (2011). Natural
inducement of hydrogen from food waste by temperature control. International Journal Of
Hydrogen Energy 36(17): 10666-10673.
Kim M.-S.,Jaehwan C., and Dong-Hoon K.. (2013). Chapter 11 - Fermentative
Biohydrogen Production from Solid Wastes. Biohydrogen. P. Ashok, C. Jo-Shu, C. H.
Patrick, J.-S. C. P. C. H. Christian LarrocheA2 - Ashok Pandey and L. Christian.
Amsterdam, Elsevier: 259-283.
Kimia S. (2013). Hydrogen Synthesis.
http://kimia.um.edu.my/staff_new/sharifah_bee/2324/SCES2340_P3_Hydrogen_Synthesis
_041218.pdf.
Kraemer J. T. and Bagley D.M. (2007). Effects of Gas Sparging in Biohydrogen
Production. Biotechnology Lett 29: 685-695.
Krishnan V., Desa A., and Christianto S. (2007). Bio-hydrogen generation from mixed fruit
peelwaste using anaerobic contact filter. International Journal of Hydrogen Energy 32:
4754 – 4760.
120
Kumar A., Tormod S., Alfred A., Rodolfo C. R., Jean-Michel D., Marcos F., Douglas H.,
Ånund K., and Zhiyu L. (2011). Hydropower. IPCC Special Report on Renewable Energy
Sources and Climate Change Mitigation. O. Edenhofer, R. Pichs-Madruga, Y. Sokonaet al.
Cambridge, United Kingdom and New York, NY, USA, Cambridge University Press.
Lee K., Hsu Y., Lo Y., Lin P., Lin C., and Chang J. (2008). Exploring optimal
environmental factors for fermentative hydrogen production from starch using mixed
anaerobic microflora. International Journal of Hydrogen Energy 33: 1565 - 1572.
Lee Y-W. and Chung J. (2010). Bioproduction of hydrogen from food waste by pilot-scale
combined hydrogen/methane fermentation. International Journal of Hydrogen Energy
35(21): 11746-11755.
Lenntech B. V. (2013). Water Treatment Solutions. from
http://www.lenntech.com/periodic/elements/pb.htm#ixzz2ljMY2F5I.
Leon A. T. (2011). Health-promoting Properties of Fruit and Vegetables. Cranfield
University, UK, Cranfield University, UK.
Li J., Baikun L., Gefu Z., Nanqi R., Lixin B., and Junguo H. (2007). Hydrogen production
from diluted molasses by anaerobic hydrogen producing bacteria in an anaerobic baffled
reactor (ABR). International Journal of Hydrogen Energy 32(15): 3274-3283.
Li Z., Wanga H., Tanga Z., Wanga X., and Bai J. (2008). Effects of pH value and substrate
concentration on hydrogen production from the anaerobic fermentation of glucose.
International Journal of Hydrogen Energy 33: 7413-7418.
121
Lin C.-Y., Chein-Chung W., and Chun-Hsiung H. (2008). Temperature effects on
fermentative hydrogen production from xylose using mixed anaerobic cultures.
International Journal of Hydrogen Energy 33(1): 43-50.
Liu, G., and Shen, J. (2004). Effects of culture and medium conditions on hydrogen
production from starch using anaerobic bacteria. Journal of Bioscience and Bioengineering
98(4): 251-256. doi: http://dx.doi.org/10.1016/S1389-1723(04)00277-4
Logan B. E. and Regan J. M. (2006). Microbial fuel cells-challenges and applications.
Environmental Science and Technology 40(17): 5172-5180.
Manaf L. A., Mohd A. A. S., and Nur I. M. Z. (2009). Municipal solid waste management
in Malaysia: Practices and challenges. Waste Management 29(11): 2902-2906.
Marbán G., and Valdés-Solís T. (2007). Towards the hydrogen economy? International
Journal of Hydrogen Energy 32(12): 1625-1637.
Mars A. E., Veuskens T., Budde M. A. W., van Doeveren P. F. N. M., Lips S. J., Bakker R.
R., Claassen P. A. M. (2010). Biohydrogen production from untreated and hydrolyzed
potato steam peels by the extreme thermophiles Caldicellulosiruptor saccharolyticus and
Thermotoga neapolitana. International Journal of Hydrogen Energy 35(15): 7730-7737.
doi: http://dx.doi.org/10.1016/j.ijhydene.2010.05.063
Masirin M., Idrus M., Ridzuan M. B., and Mustapha S. (2008). An overview of landfill
management and technologies: a Malaysian case study at Ampar Tenang.
122
Massanet-Nicolau J., Dinsdale R., and Guwy A. (2008). Hydrogen production from sewage
sludge using mixed microflora inoculum: Effect of pH and enzymatic pretreatment.
Bioresource Technology 99(14): 6325-6331. doi:
http://dx.doi.org/10.1016/j.biortech.2007.12.012
Masset J., Serge H., Christopher H., Laurent B., Fabrice F., and Philippe T. (2010). Effect
of pH on glucose and starch fermentation in batch and sequenced-batch mode with a
recently isolated strain of hydrogen-producing Clostridium butyricum CWBI1009.
International Journal of Hydrogen Energy 35(8): 3371-3378.
Matthew M., Yung W., Jablonski S., Kimberly, A., Magrini-Bair. (2009). Review of
Catalytic Conditioning of Biomass-Derived Syngas. Energy and Fuels 23: 1874-1887.
Merrill G. m. L. (2010). The Effects of Temperature Stress on the Quality and Yield of
Soya Bean. Journal of Agricultural Science 2(1): 172-179.
Michael B. S., Wooshin. P., Zuoc, Y., Bruce E. L, (2006). Inhibition of biohydrogen
production by ammonia. Water Research 40: 1167 – 1172.
Millet P. and Grigoriev, S. (2013). Chapter 2 - Water Electrolysis Technologies.
Renewable Hydrogen Technologies. L. M. Gandía, G. Arzamendi and P. M. Diéguez.
Amsterdam, Elsevier: 19-41.
Mizuno O., Dinsdale R., Freda H., Dennis L. and Tatsuya N. (2000). Enhancement of
hydrogen production from glucose by nitrogen gas sparging. Bioresource Technology
73(1): 59-65.
123
Mu Y., Yu H. Q. and Wang G. (2007). A kinetic approach to anaerobic hydrogen-
producing process. Water Res 41(5): 1152-1160.
Muñoz-Páez K.M., Elvira R.L., Idania V.V., Noemí R.S., and Héctor M., Poggi-Varaldo.
(2012). Re-Fermentation of Washed Spent Solids from Batch Hydrogenogenic
Fermentation for Additional Production of Biohydrogen from the Organic Fraction of
Municipal Solid Waste. Journal of Environmental Management 95, Supplement 3: S355-
S59.
Nakahashi J. (2008). Recent life cycle assessment (LCA) activities by the Plastic Waste
Management Institute, JLCA News Letter, pp. 3–8.
Nasr N., Elsayed E., Hisham H., George N., and Hesham M.., El Naggar (2011). Bio-
hydrogen production from thin stillage using conventional and acclimatized anaerobic
digester sludge. International Journal of Hydrogen Energy 36(20): 12761-12769.
Nathao, C., Ubonrat S., and Nipon P. (2013). Production of hydrogen and methane by one
and two stage fermentation of food waste. International Journal of Hydrogen Energy 1-
6pp.
Nazlina, H. M. Y., Abd Rahman. N.’A., Che M.. Hasfalina, M. Z., Mohd Y., and Mohd
A.H.(2011). Microbial characterization of hydrogen-producing bacteria in fermented food
waste at different pH values. International Journal of Hydrogen Energy 36: 9571 - 9580.
124
Nazlina, H. M. Y.,Abd Rahman. N.’A., Che M.. Hasfalina, M. Z., Mohd Y., and Mohd
A.H (2009). Effect of Different Temperature, Initial pH and Substrate Composition on
Biohydrogen Production from Food waste in Batch Fermentation. Asian Journal of
Biotechnology1 (2): 42-50.
Nicolet Y., Cavazza C., Fontecilla-Camps J. C. (2002)Fe-Only Hydrogenases: Structure,
Future and Evolution. J Inorganic Biochemistry 91: 1-8.
Noor Z. Z., Yusuf R. O., et al. (2013). "An overview for energy recovery from municipal
solid wastes (MSW) in Malaysia scenario." Renewable and Sustainable Energy Reviews
20(0): 378-384.
O-Thong S., Prasertsan P. et al. (2007). Improvement of biohydrogen production and
treatment efficiency on palm oil mill effluent with nutrient supplementation at thermophilic
condition using an anaerobic sequencing batch reactor. Enzyme and Microbial Technology
41(5): 583-590.
Okamoto M, N. T., Miyahara T., Mizuno O. (2000). Biological hydrogen potential of
materials characteristic of the organic fraction of municipal solid wastes. Water Sci Technol
41(3): 25-32.
Omran A., Mahmood A., Abdul Aziz, H. and Robinson G .M. (2009). Investigating
Households Attitude Toward Recycling of Solid Waste in Malaysia: A Case Study.
International Journal of Environmental Research, 3(2): 275-288.
125
Outlook, I. E. (2012). International Energy Outlook. USA: U.S. Energy Information
Administration.
Pan J., Chen X., Sheng K., Yu Y., Zhang C., and Ying Y. (2013) Effect of ammonia on
biohydrogen production from food waste via anaerobic fermentation. International Journal
of Hydrogen Energy. doi: http://dx.doi.org/10.1016/j.ijhydene.2013.06.093
Pan J., Ruihong Z., Hamed M. El-M., Huawei S., and Yibin Y. (2008). Effect of food to
microorganism ratio on biohydrogen production from food waste via anaerobic
fermentation. International Journal of Hydrogen Energy 33(23): 6968-6975.
Parrot L., Sotamenou J. et al. (2009). Municipal solid waste management in Africa:
Strategies and livelihoods in Yaoundé, Cameroon. Waste Management 29(2): 986-995
Percy K. E., Hansen M. C., and Dann T. (2012). Chapter 4 - Air Quality in the Athabasca
Oil Sands Region 2011. In E. P. Kevin (Ed.). Developments in Environmental Science. 11:
47-91pp Elsevier.
Qinglan H., Chang W., Dingqiang L., Yao W., Dan L., and Guiju L. (2010). Production of
hydrogen-rich gas from plant biomass by catalytic pyrolysis at low temperature.
International Journal of Hydrogen Energy 35(17): 8884-8890. doi:
http://dx.doi.org/10.1016/j.ijhydene.2010.06.039
Rajendran K., Aslanzadeh S., and Taherzadeh M. J. (2012). Household biogas digesters—a
review. Energies 5(8): 2911-2942.
126
Ren N., Jianzheng L., Baikun L., Yong W., and Shirui L. (2006). Biohydrogen production
from molasses by anaerobic fermentation with a pilot-scale bioreactor system. International
Journal of Hydrogen Energy 31(15): 2147-2157. doi:
http://dx.doi.org/10.1016/j.ijhydene.2006.02.011
REN21. (2011). Renewables. Global Status Report, 116.
Renea R., Adriaan W., Jeremaisse M., Hubertusv H., and Ceesj B. (2007). Hydrogen
Production with a Microbial Biocathode. Environ. Sci. Technol. 42: 629–634.
Richard A. (2008). Milestone for H2 Production by High-Temperature Electrolysis
Retrieved 14/11/2013, 2013, from
http://www.greencarcongress.com/2004/11/milestone_for_h.html
Rozendal R. A., Hamelers H. V. M., Rabaey K., Keller J., and Buisman C. J. N. (2008).
Towards practical implementation of bioelectrochemical wastewater treatment. Trends in
Biotechnology 26(8): 450-459. doi: http://dx.doi.org/10.1016/j.tibtech.2008.04.008
Ruihong Z., Hamed M., E., Karl H., Fengyu W.,Guangqing L., Chris C., Paul G. (2007).
Characterization of food waste as feedstock for anaerobic digestion. Bioresource
Technology 98: 929–935.
Saeed Isa, A., Johari A., Hashim H., Mat R., and Alkali H. (2013). Landfill gas and its
renewable energy potentials in Johor,Malaysia. International Journal of Emerging Trends
in Engineering and Development 1(3): 506-520.
127
Sathaye J., Lucon O., Rahman A., Christensen J., Denton F., Fujino J., . . . Shmakin A.
(2011). Renewable Energy in the Context of Sustainable Development. In O. Edenhofer, R.
Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P.
Eickemeier, G. Hansen, S. Schlömer and C. von Stechow (Eds.), IPCC Special Report on
Renewable Energy Sources and Climate change Mitigation. Cambridge, United Kingdom
and New York, NY, USA: Cambridge University Press.
Seadon, J. K. (2006). Integrated waste management – Looking beyond the solid waste
horizon. Waste Management, 26(12): 1327-1336. doi:
http://dx.doi.org/10.1016/j.wasman.2006.04.009
Shekdar, A. V. (2009). Sustainable solid waste management: an integrated approach for
Asian countries. Waste Management 29(4): 1438-1448.
Shin H.-S., Youn J.H., and Kim S.H. (2004). Hydrogen production from food waste in
anaerobic mesophilic and thermophilic acidogenesis. International Journal of Hydrogen
Energy, 29(13): 1355-1363. doi: http://dx.doi.org/10.1016/j.ijhydene.2003.09.011
Shimizu S., Mizuno A. F., Kameda T., Yoshioka T. (2008). Fermentative Hydrogen
Production From Food Waste. Water Dynamics, American Institute of Physics
Sinha P., and Pandey A. (2011). An evaluative report and challenges for fermentative
biohydrogen production. International Journal of Hydrogen Energy 36(13): 7460-7478.
doi: http://dx.doi.org/10.1016/j.ijhydene.2011.03.077
128
Smith J. L. (2010). The Suitability of Using Food Waste as an Anaerobic Digester
Feedstock. Doctorate, University of Florida, Gainesville.
Staudt L. (2008). Chapter 6 - Wind Energy. In M. L. Trevor (Ed.), Future Energy Oxford:
Elsevier. Pp. 93-110.
Stern, N. (2006). The economics of climate change (pp. 700).
Stohs S. J., and Bagchi D. (1995). Oxidative mechanisms in the toxicity of metal ions. Free
Radical Biology and Medicine 18(2), 321-336. doi: http://dx.doi.org/10.1016/0891-
5849(94)00159-H
Sun Y. and Cheng J. (2002). Hydrolysis of lignocellulosic materials for ethanol production:
a review. Bioresource Technology 83(1): 1-11. doi: http://dx.doi.org/10.1016/S0960-
8524(01)00212-7
Tawfik A. and El-Qelish M. (2012). Continuous hydrogen production from co-digestion of
municipal food waste and kitchen wastewater in mesophilic anaerobic baffled reactor.
Bioresource Technology 114(0): 270-274.
Tomczak-Wandzel R., Levilin E. (2013). Biogas Production From Fish Waste in Co-
digestionwith Sewage Sludge. Sweden Environmental Institute. Swedish Environmental
Institute.
Troschinetz A. M. and Mihelcic J. R. (2009). Sustainable recycling of municipal solid
waste in developing countries. Waste Management 29(2): 915-923.
129
Ueno Y, H. S., Ishii M., Igarashi Y. (2001). Changes in product formation and bacterial
community by dilution rate on carbohydrate fermentation by methanogenic microflora in
continuous flow stirred tank reactor. Appl Microbiol Biotechnol 57(1-2): 65-73.
Valdez-Vazquez, I. and Poggi-Varaldo, H. M. (2009). Hydrogen production by
fermentative consortia. Renewable and Sustainable Energy Reviews 13(5): 1000-1013.
Vijayaraghavan K. and Yun Y.S. (2008). Bacterial biosorbents and biosorption.
Biotechnology Advances 26(3): 266-291. doi:
http://dx.doi.org/10.1016/j.biotechadv.2008.02.002
Voet D, Voet JG, Pratt CW. (1999). Fundamentals of Biochemistry. US: John Wiley,
Wang J. and Wan W. (2009). Factors influencing fermentative hydrogen production: A
review. International Journal of Hydrogen Energy 34(2): 799-811.
Worrell W.A., Vesilind P. A. (2012) Solid Waste Engineering. Second ed. Cengage
Learning, Stamford, CT.
Xiao L, Zhiyi D, Ka Y. Fung, and Ka M. Ng. (2013) Biohydrogen Generation from
Anaerobic Digestion of Food Waste. International Journal of Hydrogen Energy 38(32):
13907-13.
Yap S. (2013). Alkalinity For Better Health. The Sun. Malaysia: 21.
130
Yasin N. H.M., Tabassum M., Mohd Ali H., and Nor'Aini A R (2013). Food waste and
food processing waste for biohydrogen production: A review. Journal of Environmental
Management 130(0): 375-385.
Yu W, Wang H, Xiaoqiong F, Xiaofang W, Jianxin H. (2010). Biohydrogen production
from cornstalk wastes by anaerobic fermentation with activated sludge. International
Journal of Hydrogen Energy 35: 3092 – 3099.
Zhang J., and Wang Q. (2005). Buffering and nutrient effects of white mud from ammonia–
soda process on thermophilic hydrogen fermentation from food waste. International
Journal of Hydrogen Energy. doi: http://dx.doi.org/10.1016/j.ijhydene.2013.08.047
Zhao X., Defeng X., Bingfeng L., Lu L., Jun Z., and Nanqi R. (2012). The effects of metal
ions and l-cysteine on hydA gene expression and hydrogen production by Clostridium
beijerinckii RZF-1108. International Journal of Hydrogen Energy 37(18): 13711-13717.
Zheng X-J. and Han-Qing, Y. (2005). Inhibitory effects of butyrate on biological hydrogen
production with mixed anaerobic cultures. Journal of Environmental Management 74(1):
65-70.
Zhu G. F., Jiang Z. L., Liu C-X. (2011). Fermentative Hydrogen Production from Soybean
Protein Processing Wastewater in an Anaerobic Baffled Reactor (ABR) Using Anaerobic
Mixed Consortia. Applied biochemistry and biotechnology 1(168): 91-105.
Zong W., Ruisong Y., Peng Z., Meizhen F., and Zhihua Z. (2009). Efficient hydrogen gas
production from cassava and food waste by a two-step process of dark fermentation and
photo-fermentation. Biomass and Bioenergy 33(10): 1458-1463.
131